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Abstracts By Presenter's Last Name

A

Gabriella Alvarez

Observations of the Abell 3391/Abell 3395 Intercluster Filament

Presenter: Gabriella Alvarez, Center for Astrophysics/Vanderbilt

Session: Poster

Additional Authors: S.R. Randall, H. Bourdin, C. Jones, K.H. Holley-Bockelmann
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         We present \textit{Chandra} and \textit{XMM-Newton} X-ray observations of the Abell 3391/Abell 3395 intercluster filament. It has been suggested that the galaxy clusters Abell 3395, Abell 3391, and the galaxy group ESO-161 located between the two clusters, are in alignment along a large-scale intercluster filament. We find that the filament is aligned close to the plane of the sky, in contrast to previous results. We find a global projected filament temperature kT = $4.45_{-0.55}^{+0.89}$~keV, electron density $n_e=1.08^{+0.06}_{-0.05} \times 10^{-4}$~cm$^{-3}$, and $M_{\rm gas} = 2.7^{+0.2}_{-0.1} \times 10^{13}$~M$_\odot$. The thermodynamic properties of the filament are consistent with that of intracluster medium (ICM) of Abell 3395 and Abell 3391, suggesting that the filament emission is dominated by ICM gas that has been tidally disrupted during an early stage merger between these two clusters. We find that the galaxy group ESO-161 may be undergoing ram pressure stripping in the low density environment at or near the virial radius of both clusters due to its rapid motion through the filament.

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Jake Arthur

The impact of complex baryonic processes on simulated galaxy clusters

Presenter: Jake Arthur, University of Nottingham

Session: Poster

         Hydrodynamical simulations are vital tools in aiding and interpreting astronomical observations of galaxy clusters. Simulations can evolve dark matter and gas particles reasonably well, but struggle to deal with more complex baryonic processes such as star formation or AGN feedback. This is because these processes span an enormous dynamic and temporal range, and so they are often solved with tunable analytical prescriptions, namely subgrid physics. The choice and tuning of subgrid physics has a substantial effect on the global properties of any simulated galaxy cluster, which means that it is imperative to check the validity of a simulation's choice of subgrid physics before reliable conclusions may be drawn. I will present data from the `nIFTy cluster comparison series', which compares ten different synthetic galaxy clusters at z=0, each produced by a different start-of-the-art code equipped with its own preferred subgrid physics. By using ~1000 haloes in a 5Mpc region surrounding each cluster, I will show that there is an enormous difference between the synthetic galaxy populations and properties produced by each code. Along with this, I will show that all codes cannot reproduce observed global stellar fractions across all dark matter halo masses, and that these effects are a direct consequence of the employed subgrid physics rather than any environmental effect. To conclude, I will briefly touch upon how we can use reliably simulated galaxy clusters to study their formation by accurately tracking their gas content.

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B

David Barnes

Exploring the Formation & Destruction of Cool-Cores with IllustrisTNG

Presenter: David Barnes, MIT

Session: Cool Cores I: Statistics, Formation and Destruction
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         Galaxy clusters form via a hierarchical series of mergers between increasingly massive collapsed haloes. Simultaneously the environment of these haloes is continually shaped by energetic astrophysical processes, like feedback from active galactic nuclei. The thermal structure of the intracluster medium (ICM), such as the presence of a cool-core, is a sensitive window into the balance between merging events and ongoing astrophysical processes. Current and impending observational facilities, like Chandra, Suzaku, SPT-3G and eRosita, are beginning to probe the thermal structure of the ICM over 10 Gyrs of cosmic time, providing a detailed picture of the formation of galaxy clusters. Recently there have been significant advances in our theoretical modelling of structure formation and state-of-the-art simulations now yield large cosmologically-representative volumes that match a wide range of observations. In this talk, I will explore the formation and destruction of cool-cores using the IllustrisTNG simulations (Weinberger et al. 2017, Pillepich et al. 2018), specifically focusing on the TNG300 level 1 volume that contains 370 groups and clusters with log(M500/Msun) > 13.75. I will compare the fraction of IllustrisTNG systems that host a cool-core to the observed fraction in unbiased samples for a range of cool-core criteria and how both simulated and observed cool-core fractions evolve with redshift (Barnes et al. 2017). I will then explore the conditions required for cool-cores to form in a cosmological simulation and the mechanisms that lead to their destruction (Barnes et al in prep.). Finally, I will demonstrate that missing physical processes, like anisotropic thermal conduction, can alter the simulated cool-core fraction and improve the match to observations.

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Iacopo Bartalucci

XMM & Chandra Combined Analysis of the Most Massive Galaxy Clusters at z~1

Presenter: Iacopo Bartalucci, CEA

Session: Distant clusters

Additional Authors: Monique Arnaud, Gabriel Pratt
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         We present a detailed study of the spatially resolved thermodynamic and hydrostatic mass profiles of the five most massive clusters detected at z~1 via the Sunyaev-Zel'dovich effect. These objects represent an ideal laboratory to test our models in a mass regime where structure formation is driven mainly by gravity. We present a method to study these objects that optimally exploits information from XMM-Newton and Chandra observations. The combination of Chandra’s excellent spatial resolution and XMM-Newton’s photon collecting power allows us to spatially resolve the profiles from the core to the outskirts, for the first time in such objects. Evolution properties are investigated by comparison with the REXCESS local galaxy cluster sample and prediction from numerical simulations. Finally, we discuss the current limitations of this method in the context of joint analysis of future Chandra and XMM large programs and, more generally, of multi-wavelength efforts to study high redshift objects.

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Kaustuv Basu

SZ Observations of Cluster (Relic) Shocks

Presenter: Kaustuv Basu, University of Bonn

Session: SZ
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         In this presentation I will summarize the current status of the Sunyaev-Zel'dovich (SZ) effect measurements of merger and accretion shocks in galaxy clusters, plus what we can expect down the road within the next 5 to 10 years. I will be paying specific attention to the measurement of shocks underlying radio relics, to highlight the advantage of SZ measurement for these class of objects, and the physics that can be learned from a cross-comparison of the SZ, X-ray and radio synchrotron data. I will conclude by highlighting a list of recent SZ shock observations and their scientific results, including the most famous example of all: the bow shock in the Bullet cluster.

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Kaustuv Basu

SZ Science From 5600m: the New CCAT-Prime Sub-Millimeter Telescope

Presenter: Kaustuv Basu, University of Bonn

Session: Future Instruments
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         CCAT-prime is a new 6 m diameter sub-millimeter telescope at 5600 m altitude in Chile, which is currently being built and will start observing in 2021. One of its primary science objective is to survey a large area of the sky (~10k square deg) in multiple frequency bands for the Sunyaev-Zel'dovich (SZ) effect. An unique optical design enables a very large field-of-view (up to 8 degrees at 3 mm) and correspondingly large bolometer arrays, which will provide unprecedented sensitivities for carrying out a wide range of cluster SZ science. Furthermore, the excellent location at 5600 m altitude enables high-frequency channels up to 0.35 mm that are critical for the separation of multiple SZ-components (tSZ, kSZ, and rSZ effects) and removal of foregrounds. I will present here an overview of the various SZ science topics that are being considered in preparation of the first light from the CCAT-prime telescope.

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Nicholas Battaglia

On Cluster Profiles with CMB-S4

Presenter: Nicholas Battaglia, CCA Flatiron Inst. / Cornell

Session: SZ
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         The next generation cosmic microwave background (CMB) experiment, CMB-S4, will make unprecedented measurements of secondary anisotropies in the CMB. I will focus on observations of the thermal and kinetic Sunyaev-Zel’dovich (SZ) effects, which will provide new windows into the thermodynamic properties of galaxy groups and clusters. I will show how we can constrain important baryonic processes, like feedback, that govern group and cluster formation through the high fidelity SZ profile measurements from CMB-S4. Additionally, I will describe the prospects to constrain fundamental physics from SZ observations and how to mitigate the modeling uncertainties associated with the baryonic processes that currently limit these constraints.

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Matthew Bayliss

The Chandra Strong Lens Sample

Presenter: Matthew Bayliss, MIT

Session: Poster
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         I will describe the Chandra Strong Lens Sample, a new sample of 29 galaxy clusters selected purely on their strong gravitational lensing signatures. The strong lensing selection ensures uniform availability of both Chandra ICM measurements and strong lens models of the total mass content in cores of all 29 clusters. Furthermore, the strong lensing selection can be trivially reproduced in simulations, enabling direct comparisons between the observed and simulated ICM properties and scaling relations of strong lensing selected clusters. Astrophysical processes that generate high cross-section strong lensing clusters should also manifest as biases in standard mass proxy scaling relations. We can look for these signatures and quantify the magnitude of their impact by comparing scaling relations of this strong lensing selected sample against other samples selected based on mass-proxies (e.g., SZ, X-ray, optical richness).

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Stefano Borgani

Reconstructing ICM Thermo- & Chemo-Dynamics with Simulations

Presenter: Stefano Borgani, INAF & University of Trieste

Session: Advances in Simulations
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         I will present results from cosmological hydrodynamic simulations of galaxy clusters aimed at describing the evolution of the ICM thermo- and chemo-dynamical properties. In particular I will focus on two main aspects: (1) how the properties of the ICM in the cluster outskirts can be used as fossil records of the past history and nature of feedback; (2) what multi-wavelength observations of proto-clusters at z~2-3 can tell us about the physical mechanisms that determined the low-redshift cluster properties.

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Andrea Botteon

Abell 1758: a Double Radio Halo System Discovered with LOFAR

Presenter: Andrea Botteon, IRA-INAF - Università di Bologna

Session: Nonthermal Phenomena II

Additional Authors: LOFAR Surveys KSP Collaboration
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         A number of merging galaxy clusters show the presence of diffuse radio emission on the Mpc-scale in the intra-cluster medium (ICM). Major mergers are believed to play a role in the formation of radio halos and radio relics through complex mechanisms involving the dissipation of turbulence and shocks in the ICM. Nonetheless, the physical processes that generate these steep synchrotron spectrum sources are still poorly constrained. A step forward in our understanding of non-thermal phenomena in galaxy clusters is expected from LOFAR, a revolutionary radio telescope that is opening a new observational window at the low frequency. I will present the results from a LOFAR Tier 1 observation at 150 MHz of the double galaxy cluster A1758. This system is in a complex dynamical state and is constituted by two main components, A1758N and A1758S, separated by a projected distance of about 2 Mpc. A1758N is a massive cluster hosting a known giant radio halo while A1758S is less massive and no diffuse radio emission in this cluster was previously known. Our LOFAR observation revealed the presence of radio halos in both clusters, a possible emission along the bridge connecting the two systems and a candidate radio relic in A1758S. We combined our LOFAR data with archival VLA and GMRT observations to constrain the spectral properties of the halos and candidate relic. We also analyzed a deep archival Chandra observation and suggest that A1758N and A1758S are in a pre-merger phase. The ICM temperature across the tentative bridge of radio emission connecting the two sub-clusters shows a drop possibly indicating the presence of a transversal shock generated in the initial stage of the merger.

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Andrea Botteon

New detections of merger shocks & cold fronts in galaxy clusters

Presenter: Andrea Botteon, IRA-INAF - Università di Bologna

Session: Poster

Additional Authors: Fabio Gastaldello, Gianfranco Brunetti
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         Galaxy cluster mergers are among the most energetic phenomena in the Universe and lead to significant perturbation of the intra-cluster medium (ICM). The most striking features of a merger in a cluster X-ray image are sharp discontinuities due to shocks and cold fronts, classified on the base of the sign of the temperature jump across the edge. The observation of these fronts allows to study important aspects of the ICM microphysics, such as its thermal conduction and viscosity, as well as to provide information on the physical conditions leading to the acceleration of cosmic rays and magnetic field amplification in the cluster environment. However, the number of detected edges in clusters is small due to observational limitations. We present the results of a search for new shocks and cold fronts in a sample of 15 merging and massive galaxy clusters observed with Chandra. We used different imaging and spectral techniques of X-ray observations to properly characterize the edges distinguishing shocks from cold fronts. Our analysis led to the discovery of 22 edges: 6 shocks, 8 cold fronts and 8 with uncertain origin. All the 6 shocks detected have Mach < 2 derived from density and temperature jumps. This work contributed to increase the number of discontinuities detected in clusters and shows the potential of combining diverse approaches aimed to identify edges in the ICM.

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Marusa Bradac

The Final Frontier of Galaxy Formation with Galaxy Clusters as Cosmic Telescopes

Presenter: Marusa Bradac, UC Davis

Session: Galaxies in and Behind Clusters
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         In the recent years HST observations of blank fields enabled us to detect galaxies as far as z~11. However, very little is known about those galaxies, and they are mostly the most luminous representatives. Clusters of galaxies, when used as cosmic telescopes, can greatly simplify the task of studying and finding normal galaxies at high redshifts. In particular, they allow us to see galaxies that are likely beacons of the epoch of reionization, which marked the end of the so-called ``Dark Ages'' and signified the transformation of the universe from opaque to transparent. With a massive cluster one can gain several magnitudes of magnification over a typical observing field, enabling imaging and spectroscopic studies of intrinsically lower-luminosity galaxies that would otherwise be unobservable, even with the largest telescopes. Several large surveys have recently been executed (CLASH, HFF, Relics with HST, SURFS UP for Spitzer imaging, GLASS for HST spectroscopy) with the main goal of identifying and studying star formation of galaxies at z=1-11. I will present results from these surveys and show successful measurements of the properties of stellar populations at z~7 and beyond.

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Marusa Bradac

A New Look at Galaxy Clusters with JWST

Presenter: Marusa Bradac, UC Davis

Session: Future Instruments
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         TBD

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Marcus Bruggen

Shocks & Turbulence in Clusters: Insights From Radio Observations

Presenter: Marcus Bruggen, University of Hamburg

Session: Nonthermal Phenomena II

         Low-frequency radio observations have provided new insights into the physics of shocks and turbulence in the intracluster medium. Ultra-steep sources appear to be common and new types of diffuse sources have been found. New puzzles have also come up. They include the relationship between diffuse radio sources and radio galaxies and the efficiency of shock acceleration.

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Gianfranco Brunetti

Turbulent Acceleration & Cluster-Scale Radio Emission

Presenter: Gianfranco Brunetti, IRA-INAF

Session: Nonthermal Phenomena II

         Turbulent acceleration in galaxy clusters is a reference mechanism to explain the origin of cluster-scale radio emission. In this talk I will discuss recent results on the physics of acceleration and propagation of relativistic particles in a turbulent intra-cluster-medium, and the expected polarization properties of diffuse radio emission that is generated by these mechanisms. Prospects for LOFAR, SKA , Athena and their synergies will also be discussed.

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David Buote

Mass Profiles of Massive “Fossil” Elliptical Galaxies

Presenter: David Buote, University of California, Irvine

Session: Mass Profiles and Maps
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         I describe the mass profiles of two massive elliptical galaxies determined from X-ray observations, with an emphasis on the evidence for high concentration parameters. The first, NGC 6482, is a well-known X-ray fossil group. The second, Mrk 1216, is a massive relic galaxy thought to be a largely untouched descendent of the high-redshift red nugget population.

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Becky Canning

AGN in Clusters Up To z=2

Presenter: Becky Canning, Stanford University/KIPAC

Session: Galaxies in and Behind Clusters
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         A critical prerequisite for both AGN activity, and the formation of new stars in host galaxies, is the availability of gas. The cluster environment affects gas reservoirs in galaxies through processes such as ram-pressure stripping, evaporation, starvation, and tidal effects of the cluster potential. The density of cluster members and their relative velocities also depend on the cluster mass. As such, the rates of violent processes will differ in clusters and the field. The relative importance of these processes depends on both the position within, the mass of, and the redshift of the host galaxy cluster. I will share new results of the X-ray and Radio AGN distribution in the highest-z clusters and detail our survey which will identify ~40,000 AGN and aims to trace the evolution of AGN in dense environments from early-times, through the peaks of AGN and SF activity, to the present day.

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Damiano Caprioli

Diffusive Shock Acceleration & Beyond

Presenter: Damiano Caprioli, University of Chicago

Session: Nonthermal Phenomena II
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         I present results of large 2D and 3D hybrid (kinetic ions-fluid electrons) simulations of ion acceleration at non-relativistic collisionless shocks: injection and acceleration of ions with arbitrary mass-to-charge ratios are characterized in detail as a function of shock inclination and strength and compared with predictions of diffusive shock acceleration theory. Moreover, with the same ab-initio techniques, I investigate the re-acceleration of pre-energized “seed” particles and discuss the relevant plasma instabilities driven by energetic ions, which lead to a significant rearrangement and amplification of the background magnetic field. Finally I discuss how this “diffusive shock re-acceleration” produces peculiar spectral features that deviate from standard theoretical predictions, especially for quasi-perpendicular shocks.

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I-Non Chiu

Baryon Content in a Sample of 91 Galaxy Clusters Selected by the South Pole Telescope at 0.2<z<1.25

Presenter: I-Non Chiu, ASIAA

Session: Samples and Scaling Relations I

Additional Authors: J. J. Mohr, M. McDonald, S. Bocquet, S. Desai, M. Klein, H. Israel, M. L. N. Ashby, A. Stanford, B. A. Benson, M. Brodwin
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         In this talk, I will present a study of baryon content in galaxy clusters based on an approximately mass-limited sample of 91 clusters selected by the South Pole Telescope (SPT) at 0.2 < z < 1.25.For each cluster, the total mass (M500) is estimated by the SZE observable characterized by the SPT, the ICM mass (Micm) is obtained with the X-ray observation followed up by the Chandra, and the stellar mass (Mstar) is derived using the optical photometry from the Dark Energy Survey in combination with the Near Infrared photometry from either the WISE or the Spitzer.We then study the scaling relations of the stellar mass, ICM mass and the total baryon mass to investigate their dependence on the cluster mass and redshift.We find significant departures from self-similarity in the mass scaling for all quantities, while the redshift trends are all statistically consistent with zero, indicating that the baryon content of clusters at fixed mass has changed remarkably little over the past ~9 Gyr.We compare our results with the mean cosmic values estimated in the field, and find that those field values lie above (below) the baryon fraction (stellar mass fraction) of the cluster virialized region at all but are statistically comparable with the most massive clusters.We construct a toy model that characterizes the growth of the parent cluster by the infall from the field and from the subclusters with lower masses, and find that the existence of a fractional infall from the field could explain the strong mass-dependence of the stellar mass scaling relation while keeping the redshift trend statistically consistent with zero.Similar analysis of the ICM and total baryon mass scaling relations provides evidence of the so-called 'missing baryons' outside the cluster virialized region.This work provides the largest cluster sample to date with the uniform multi-wavelength data and the consistent methodology in estimating the total and baryonic mass for each cluster, and significantly suppress the statistical and systematic uncertainties to uncover the nature of cluster formation.

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I-Non Chiu

Weak Lensing Measurements of Magnification Bias around the optically selected galaxy clusters at 0.2 < z < 1.0 from the Hyper Suprime-Cam Survey (HSC) Subaru Strategic Survey

Presenter: I-Non Chiu, ASIAA

Session: Poster

Additional Authors: Keiichi Umetsu

         The team of the HSC survey is carrying out the multi-band (grizY) imaging over an area of 1400 deg2 with the 8.2m Subaru Telescope. The unprecedentedly deep (5 sigma limiting magnitude of a 2 arcsec diameter aperture: i~26 mag) imaging uniformly over a large area with the excellent seeing (median seeing of 0.6 arcsec in the i-band) will deliver the breakthrough science to the community, especially in the current era prior to the LSST. In this work, we present the lensing measurements of the magnification bias effect around the optically selected galaxy clusters out to redshift z ~ 1 in the first year coverage of ~140 deg2 in the HSC survey. We then utilize these lensing magnification measurements to calibrate the richness to mass scaling relation of galaxy clusters. The background sources are selected in the color-color space with the goal of sampling the background galaxies at redshift z ~ 1.5. The lensing magnification of the background sample is measured by stacking over 3600 clusters in different richness and redshift bins. We carefully quantify the contamination and the masking effect due to cluster members, and correct them in the joint modelling in a Bayesian framework. The observed lensing signal is also verified by performing the null test on another flux-limited background sample where the magnification-induced growth of the population at the faint end is in balance with the angular expansion on the sky. This work demonstrates an important and complementary method in calibrating the cluster mass independently of the shear-based analysis.

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Tracy Clarke

Mining the Sky for Cluster Radio Emission: Prospecting with VLITE

Presenter: Tracy Clarke, Naval Research Laboratory

Session: Future Instruments

Additional Authors: Simona Giacintucci (NRL), Wendy Peters (NRL)
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         I will give a brief overview of a new commensal low frequencycapability that the US Naval Research Laboratory has enabled on theNRAO Jansky Very Large Array (VLA). The VLA Low-band Ionosphere andTransient Experiment (VLITE) operates 24/7 during nearly all PI-ledVLA observing programs, recording over 6000 hours per year in a 64 MHzband centered on 352 MHz. After 3 years of operation, VLITE hassurveyed 90% of the sky above declinations of -40 degrees to depths ofat least 30 seconds. VLITE images are sensitive to emission on scalesup to 1 degree, have resolutions of 5" to 3', and have noise levels inthe range of 300 microJy/bm to 10 mJy/bm. I will present current VLITEobservations of well-known clusters and discuss the prospects of thecommensal VLITE program for cluster astrophysics.

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Tracy Clarke

Ultra-Steep Spectrum Sources in Clusters

Presenter: Tracy Clarke, Naval Research Laboratory

Session: Nonthermal Phenomena III

Additional Authors: S. Giacintucci (NRL), Emily Richards (NRC), Scott Randall (CfA), Tony Mroczkowski (ESO), Elizabeth Blanton (BU), Huib Intema (Leiden Observatory), Craig Sarazin (UVa)
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         I will present new low frequency VLA and GMRT observations of diffuseultra-steep spectrum (USS) radio emission in clusters. Radioobservations of the unusual USS source in Abell 2443 revealed that thecluster is host to an unusual extended source connected tomorphologically disturbed X-ray emission. I will present new VLA and GMRTobservations highlighting the connection of the extended radioemission to the X-ray emitting ICM. Using A2443 as a template, we havebegun a new GMRT and XMM campaign to study USS-host clusters in severalother systems that displayed similar morphological disturbances andspectral properties.

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Thomas Connor

Tying Clusters Onto the Cosmic Web with X-rays

Presenter: Thomas Connor, Carnegie Observatories

Session: Cluster Outskirts

Additional Authors: John Mulchaey, Alexey Vikhlinin, Daniel D. Kelson, Shannon Patel

         Galaxy clusters are, by baryonic mass, mostly reservoirs of hot, X-ray emitting gas. From a large-scale structure perspective, however, they are nodes in the filamentary cosmic web. While a number of studies have sought to obtain absorption line measurements of the properties of filaments, seeing these filaments in emission has been an elusive quest, due to the combination of low densities and relatively cool temperatures. Near galaxy clusters, these filaments should be easier to see as their gas properties transition to that of the cluster itself. Here, we discuss recent work on observing cluster-feeding filaments not associated with any ongoing merger around a single cluster. This work combined ultra-deep Chandra observations and a comprehensive spectroscopic campaign covering 1000's of galaxies to independently map the gas and galaxy content of a cluster.

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Virginia Cuciti

Radio Halos in Galaxy Clusters: New Statistical Constraints From the Largest Unbiased Mass-Selected Sample

Presenter: Virginia Cuciti, University of Bologna, INAF-IRA

Session: Nonthermal Phenomena I
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         Radio observations reveal the presence of diffuse Mpc scale synchrotron emission in a fraction of merging galaxy clusters. In the current picture, these sources, known as radio halos, form through the re-acceleration of electrons in the ICM by means of merger-driven turbulence. Although many aspects of the microphysics of the ICM are still unclear, present day models for the formation of radio halos allow basic predictions. Large unbiased samples of galaxy clusters with adequate radio, X-ray and SZ data are necessary to test these predictions. We selected 75 clusters with M>6x10^{14} Msun and z=0.08-0.33 from the Planck SZ catalogue and followed-up these clusters with deep radio GMRT and JVLA observations to check for cluster-scale emission. This is the largest mass-selected sample of clusters with deep radio observations and complementary X-ray data available to date. The data analysis is complete allowing us to derive statistically solid constraints on the occurrence of radio halos in clusters and on the connection between cluster dynamics and cluster scale emission. I will show how clusters are distributed in the radio-halo luminosity vs mass diagram and discuss the constraints on the evolution timescales of radio halos in galaxy clusters and on the intrinsic scatter in the emissivity of halos. These measurements provide fundamental information on the origin of these radio sources. For the very first time, we are also able to measure the occurrence of radio halos in clusters as a function of cluster mass and dynamics, concluding that such occurrence declines at smaller masses, where an increasing fraction of merging systems without radio halos is found. I will show that these findings are in agreement with the expectations of turbulent re-acceleration models and this leads to the prediction that a significant fraction of the radio quiet merging clusters in our sample hosts very steep spectrum halos that will be detected by future observations with LOFAR and MWA.

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Francesco de Gasperin

Galaxy Clusters at Ultra-Low Frequencies

Presenter: Francesco de Gasperin, Hamburg University

Session: Nonthermal Phenomena III
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         In recent years radio telescopes such as LOFAR and MWA started to explore the ultra-low frequency regime (<100 MHZ). In this presentation I will review the challenges and possibilities that this new frequency range opens for the study of galaxy clusters. As an example of the potential of this new observational window, I will discuss the recent discovery of the ultra-steep spectrum sources named Gently Re-Energized Tails (GReETs). This type of sources bridges AGN activity with merger-induced radio emission. Their existence have implications on the production and maintenance of a population of mildly relativistic electrons in the intra-cluster medium, and in turn can help explaining the formation of giant radio halos and relics.

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Martijn de Vries

Detection of non-thermal X-ray emission in the lobes & jets of Cygnus A

Presenter: Martijn de Vries, University of Amsterdam

Session: Poster

Additional Authors: Michael W. Wise, Daniela Huppenkothen, Paul E. J. Nulsen, Bradford Snios, Martin J. Hardcastle, Mark Birkinshaw, Diana M. Worrall, Ryan T. Duffy, Brian R. McNamara
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         We present a spectral analysis of the lobes and X-ray jets of Cygnus A, using more than 2 Ms of $\textit{Chandra}$ observations. The X-ray jets are notably different from the radio jets, as they are misaligned with the radio jets and are significantly wider. We detect non-thermal emission components in both lobes and jets. On the eastern side, we find 1 keV flux densities of $71_{-10}^{+10}$ nJy and $24_{-4}^{+4}$ nJy, and photon indices of $1.72_{-0.03}^{+0.03}$ and $1.64_{-0.04}^{+0.04}$ for the lobe and jet respectively. On the western side, we find flux densities of $50_{-13}^{+12}$ nJy and $13_{-5}^{+5}$ nJy, and photon indices of $1.97_{-0.10}^{+0.23}$ and $1.86_{-0.12}^{+0.18}$ for the lobe and jet respectively. Using these results, we modeled the electron energy distribution of the lobes as a broken power law with an age break. We find that a significant population of non-radiating particles is required to account for the total pressure of the eastern lobe. In the western lobe, no such population is required and the low energy cutoff to the electron distribution there needs to be raised to obtain pressures consistent with observations. This discrepancy is a consequence of the differing X-ray photon indices, which may indicate that the turnover in the inverse-Compton spectrum of the western lobe is at lower energies than in the eastern lobe. In the X-ray jets, we tested an inverse-Compton relic jet model by modeling the electron distribution in a similar way. However, poor constraints on the electron distribution and particle content of the X-ray jets make the pressures very uncertain. We find that an inverse-Compton relic jet could be close to achieving pressure balance with the surrounding lobe, although this would not be able to explain the existence of brightness inhomogeneities in the X-ray jet.

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Gabriella Di Gennaro

Radio - X-ray Observations at Galaxy Cluster Shock

Presenter: Gabriella Di Gennaro, Smithsonian Astrophysical Observatory

Session: Nonthermal Phenomena II

Additional Authors: Reinout van Weeren, Felipe Andrade-Santos, Scott Randall, Huub Rottgering, Willam Forman, Christine Jones
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         Galaxy clusters form by accretion of gas and by mergers with other clusters and galaxy groups. They reveal their presence by means of diffuse radio emission (i.e. relics and halos) and disturbed X-ray morphologies. Despite recent progress our understanding of the physics behind these collisions, there are still many open questions regarding the nature of the (re-)acceleration mechanisms, the thermodynamic properties of the hot plasma, and the dynamic of the merger scenarios. Here we present a new deep Chandra observation (400 ks) of ZwCl0008.8+5215, for which we found a clear presence of X-ray discontinuities and a “comet head” being a well-defined sub-cluster core, similar to the one seen in the Bullet Cluster. Moreover, a double radio relic has been detected at cluster shocks, in west and east direction. The western relic does not trace the full extent of the shock, which is challenging for the current (re-)acceleration mechanisms.

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Klaus Dolag

Galaxy Clusters From the Magneticum Simulations

Presenter: Klaus Dolag, University Observatory, LMU

Session: Advances in Simulations
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         Recent, cosmological hydrodynamical simulations can cover very large dynamical ranges in the resolved structures, while following a large variety of physical processes (e.g. star-formation, chemical enrichment, AGN feedback) which are important for the formation of galaxies and galaxy clusters. I will present the results from the "Magneticum" set of cosmological simulations with special emphasis on galaxy clusters. I will present results connecting the shape of the underlying dark matter halo, the ICM and the stellar component to the formation history of the halos.

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Edmund Douglass

Gas Sloshing Spirals in Non-Cool Core Clusters

Presenter: Edmund Douglass, SUNY-Farmingdale, AMNH

Session: Poster
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         Spiral-shaped regions of enhanced ICM surface brightness are found in some of the most relaxed systems in the Universe (e.g. A 2029). The formation of such spirals is attributed to the sloshing of a dense cool core (CC) about the bottom of the cluster's gravitational potential well. The process is initiated by an off-axis encounter with a subcluster and is found to leave the CC fairly intact. Recent identification of cluster-wide spirals in non-cool core (NCC) clusters (A1763, A2142), however, suggests that more violent off-axis mergers may be capable of inducing core sloshing to the point of CC destruction. To further investigate this phenomenon we have analyzed a sample of systems with intermediate core entropy ( 50 keV cm2 < K0 < 250 keV cm2) which do not appear to be undergoing major head-on mergers. We find numerous instances of what may be considered “ghost spirals” at the centers of the clusters, likely to have formed in conjunction with CC destruction. Such findings expand our understanding of the dynamical path to NCC formation and suggest that off-axis mergers play a greater role in establishing the CC-NCC cluster dichotomy than previously assumed.

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Jim Drake

Wave generation & heat flux suppression in astrophysical plasma systems

Presenter: Jim Drake, University of Maryland, College Park

Session: Poster

Additional Authors: G. T. Roberg-Clark, C. S. Reynolds and M. Swisdak
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         Understanding the thermodynamic state of the hot intracluster medium(ICM) in a galaxy clusters and other astrophysical systems requires anunderstanding of transport properties such as thermal conduction andthe associated heat flux. Thermal conduction specifically is onlypoorly understood in the weakly collisional domains where fluctuatingelectric and magnetic fields driven by the heat flux might scatterelectrons. We use particle-in-cell simulations carried out in a systemwith a sustained temperature gradient and analytic analysis to explorethe dynamics of heat-flux driven instabilities and associated heatflux suppression. In the high-beta limit relevant to galaxy clusterswhistler waves are driven unstable by electron heat flux and act asscattering centers moving at the whistler phase speed. Heat flux isstrongly suppressed. A surprise is that the limiting heat flux isnearly independent of the ambient temperature gradient and scales onlyweakly with the electron temperature, a significant departure fromthe classical Spitzer scaling. This scaling law has recently been confirmedby observations in the ambient solar wind. At lower values of betawhistler generation is suppressed and the scattering is dominated bydouble-layers, regions of intense but localized parallel (to theambient magnetic field) electric field that are able to reflect hotstreaming electrons. The impact of the weak scaling of the limitingheat flux with temperature on the thermal stability of galaxy clustersis being explored.

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Dominiqe Eckert

The XMM Cluster Outskirts Project

Presenter: Dominiqe Eckert, Max-Planck-Institute for Extraterrestrial Physics

Session: Cluster Outskirts

Additional Authors: S. Ettori, V. Ghirardini, E. Pointecouteau, S. Molendi
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         The XMM Cluster Outskirts Project (X-COP) is a very large program on XMM-Newton to advance our understanding of the physical processes taking place in the outskirts of massive clusters. The project targets a sample of 13 nearby clusters selected according to their high signal-to-noise in the Planck survey. I will present the main results of the project, focusing on the thermodynamic properties of the ICM, hydrostatic mass profiles and gas mass fraction, non-thermal pressure, accretion of substructures and metal enrichment.

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Jens Erler

Planck’s view on the spectrum of the Sunyaev-Zeldovich Effect

Presenter: Jens Erler, Argelander-Institute for Astronomy / University of Bonn

Session: Poster

Additional Authors: Kaustuv Basu, Jens Chluba & Frank Bertoldi
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         The Sunyaev-Zeldovich (SZ) effect is a spectral distortion of the cosmic microwave background (CMB) due to inverse Compton scattering of CMB photons by free electrons of the hot intracluster medium (ICM). Its signal is proportional to the line of sight integral of the thermal gas pressure and not dimmed with redshift. The SZ effect has been used extensively in the last two decades to detect and characterize galaxy clusters and has become an important tool for cosmology. Due to the high temperatures of several keV found in the ICM, relativistic effects are expected to distort the SZ spectrum allowing to measure the temperature of the scattering gas. We attempt to measure these relativistic distortions by performing a stacking analysis of a large sample of galaxy clusters with data from the Planck mission. With its nine frequency channels, Planck allows to probe the entire spectrum of the SZ, making it ideally suited for this study. Of particular interest are high frequencies from 353 to 857 GHz where the relativistic corrections are strongest but that are difficult to access with ground-based observatories.The main challenge in utilizing these frequencies is to separate the SZ signal from much brighter galactic foregrounds as well as far infrared emission from the clusters themselves. The talk will be concluded by an outlook on the upcoming CCAT-prime telescope, which will improve upon Planck with lower noise and better spatial resolution.

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August Evrard

Property Covariance in Massive Halos

Presenter: August Evrard, U Michigan

Session: Samples and Scaling Relations II

Additional Authors: Arya Farahi, Ian McCarthy, David Barnes, Scott Kay, Devon Hollowood, Tesla Jeltema, Kathy Romer (+DES Cluster WG)

         Property Covariance in Massive Halos Scaling relations - the statistical relationships among multiple, observable properties of the galaxy cluster population - lie at the nexus of astrophysical and cosmological studies with clusters. I show that recent BAHAMAS and MACSIS simulations with AGN feedback offer strong support for a log-normal model of multi-property statistics in the massive halo population. In particular, a cosmologically-motivated population model achieves one percent accuracy in estimating log-mean halo mass at a fixed observable (Mgas or Mstar), paving the way for future applications to large survey samples. Shifting to empirical studies under this model framework, I describe ongoing efforts to use X-ray data to constrain the scatter in total mass at fixed optical richness for the DES-Y1 redMaPPer cluster sample. In both studies, the importance of understanding the full covariance among multiple cluster properties is emphasized.

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Thomas Fish

Assessing the stagnation point method through simulation of NGC 1404

Presenter: Thomas Fish, Harvard-Smithsonian Centre

Session: Poster

Additional Authors: Elke Roediger, Ralph P. Kraft, Yuanyuan Su, Alexander Sheardown, Matthew Hunt, William Forman, Christine Jones, Paul Nulsen, Eugene Churazov
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         When an elliptical galaxy or a subcluster moves through the ICM of its host cluster, the ICM pressure is enhanced at the upstream stagnation point. In principle, the galaxy’s or subcluster's velocity can be derived from this pressure enhancement. This stagnation point method has been applied to numerous observed examples, however, the standard method takes into account hydrodynamical effects only. We test this method on a full hydro + N-body simulation of the elliptical galaxy NGC 1404 moving through the Fornax cluster, using both the Bernoulli equation and an extension that takes into account an adiabatic shock jump. We find that the true stagnation point pressure always exceeds both hydrodynamic predictions as they do not take into account an additional ICM compression by the galaxy's gravitational potential. Thus, if the enhanced stagnation point pressure is attributed solely to the galaxy’s motion, its velocity can be overestimated up to a factor of a few during subsonic motion, and still by tens of percent during supersonic motion near pericentre passage. We also find that on approaching apocentre, the method breaks down completely due to highly irregular flow patterns around the galaxy. We present an updated stagnation point method that includes the galaxy’s gravity and improves the derived velocity estimate.

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William Forman

Characterizing the Outburst of the Supermassive Black Hole in M87

Presenter: William Forman, SAO

Session: Cool Cores II: heating vs. cooling

Additional Authors: Churazov, E.; Jones, C.; Heinz, S.; Kraft, R.; Vikhlinin, A.
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         M87, the active galaxy at the center of the Virgo cluster, is ideal for studying the interaction of a supermassive black hole (SMBH) with a hot, gas-rich environment. A deep Chandra observation of M87 exhibits an approximately circular shock front (13 kpc radius, in projection) driven by the expansion of the central cavity (filled by the SMBH with relativistic radio-emitting plasma) with projected radius ˜1.9 kpc. We combine constraints from X-ray and radio observations of M87 with a shock model to derive the properties of the outburst that created the 13 kpc shock. Principal constraints for the model are (1) the measured Mach number (M ˜ 1.2), (2) the radius of the 13 kpc shock, and (3) the observed size of the central cavity/bubble (the radio-bright cocoon) that serves as the piston to drive the shock. We find that an outburst of ˜5 × 1057 erg that began about 12 Myr ago and lasted ˜2 Myr matches all the constraints. In this model, ˜22% of the energy is carried by the shock as it expands. The remaining ˜80% of the outburst energy is available to heat the core gas. More than half the total outburst energy initially goes into the enthalpy of the central bubble, the radio cocoon. As the buoyant bubble rises, much of its energy is transferred to the ambient thermal gas. For an outburst repetition rate of about 12 Myr (the age of the outburst), 80% of the outburst energy is sufficient to balance the radiative cooling.

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Massimo Gaspari

Rainfalls in Clusters & Groups: Kinematic & Thermodynamic Tracers of the Multiphase Condensation Cascade

Presenter: Massimo Gaspari, Princeton University

Session: Cool Cores III: Rain and Fountains
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         I highlight key results of our theoretical and observational campaign to unveil the multiphase gas physics in groups and clusters. In particular, I discuss a novel method to probe gas turbulence and bulk motions, which can be leveraged by the current and upcoming multiwavelength missions. High-resolution hydro simulations show the X-ray halo radiatively cools along the turbulent eddies stimulating a top-down condensation cascade, which generates co-spatial multiphase gas. As ensemble, the warm filaments and molecular clouds inherit the turbulent kinematics of the parent hot halo (with large spectral line width), as probed by Hitomi and IFU measurements. In the nuclear region, the clouds rapidly rain toward the SMBH via chaotic cold accretion (CCA), inducing large line shifts in pencil-beam observations. Eventually, CCA triggers AGN outflow feedback which re-heats the hot halos of groups and clusters in a gentle self-regulated cycle.

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Chong Ge

X-ray emission from the richest maxBCG clusters

Presenter: Chong Ge, University of Alabama in Huntsville

Session: Poster

Additional Authors: Andrea Morandi, Ming Sun, Eduardo Rozo, Neelima Sehgal, Alexey Vikhlinin, William Forman, Christine Jones, and Daisuke Nagai
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         The galaxy cluster scaling relations are very important for studying cosmology, structure formation, and baryon evolution. We use a sample of 38 richest maxBCG clusters to study the ICM-galaxy scaling relations based on X-ray and optical observations. The clusters are selected from the two largest bins of optical richness in the Planck stacking work with the maxBCG richness N 200 > 78. We analyze their X-ray properties based on the Chandra and XMM-Newton data. While the expected cluster temperatures should be 6 - 10 keV from the optical richness, the observed range extends to temperatures as low as 1.5 keV, with nearly half of systems below 6 keV. Meanwhile, they follow normal Lx − Tx and Lx − Yx relations, which suggests that they are normal X-ray clusters. However, the scatter of Lx − N and Yx − N relations are very large with more outliers towards lower luminosity. This explains the fact that the SZ signal from model expectation is higher than the observed one from optically selected clusters, and also confirms that the X-ray selected sample are brighter than the optically selected sample. The mismatches between ICM-galaxy scaling relations are mainly from the miscentering and projection problem of an optically selected sample, as well as the possible bias in hydrostatic mass and weak-lensing mass. The mismatches are much smaller when using a BCG-dominated subsample, with the outliers suffering the projection problem.

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Marie-Lou Gendron-Marsolais

Probing the Non-Thermal Emission in the Perseus Cluster with the JVLA

Presenter: Marie-Lou Gendron-Marsolais, Université de Montréal

Session: Nonthermal Phenomena I

Additional Authors: J. Hlavacek-Larrondo, R. J. van Weeren, T. Clarke, A. C. Fabian, H. T. Intema, G. B. Taylor, K. M. Blundell and J. S. Sanders
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         Jets created from accretion onto supermassive black holes release relativistic particles on large distances. These strongly affect the intracluster medium when located in the center of a brightest cluster galaxy. On the other hand, the hierarchical merging of subclusters and groups, from which clusters originate, also generates perturbations into the intracluster medium through shocks and turbulence, constituting a potential source of reacceleration for these particles. In this talk, I will present new deep multi-configuration low radio frequency (230-470 MHz) observations of the Perseus cluster from the Karl G. Jansky Very Large Array, probing the non-thermal emission from the old particle population of the AGN outflows. Our observations of this nearby relaxed cool core cluster have revealed a multitude of new structures associated with the mini-halo, extending to hundreds of kpc in size. Its irregular morphology seems to be have been influenced both by the AGN activity and by the sloshing motion of the cluster’ gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. Furthermore, I will analyze the interplay between the radio structures and the optical filaments of NGC 1275 based on new observations with the optical imaging Fourier transform spectrometer SITELLE (CFHT) of NGC 1275, the Perseus cluster’s brightest galaxy. The Perseus cluster hosts several interesting head-tail radio galaxies (NGC 1265, NGC 1272, IC310 and CR 15) on which I will also present an analysis of the morphology and spectral index distribution.

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Simona Giacintucci

Observations of Diffuse Radio Emission in Cool-Core Clusters

Presenter: Simona Giacintucci, NRL

Session: Nonthermal Phenomena I

Additional Authors: M. Markevitch, R. Cassano, T. Venturi, T. Clarke, G. Brunetti
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         Small-scale diffuse radio sources, called minihalos, are found in cool cores of undisturbed clusters. These sources reveal a population of ultra-relativistic electrons coexisting with the intracluster thermal gas. It is unclear what these sources are, including the origin of the seed particles and their acceleration mechanism. In this talk, I will present results of our recent statistical study of minihalos and their correlation with the X-ray and SZ properties of the cluster hosts. Several interesting systems with detailed radio spectral maps also point to the likely source of seed electrons. Our findings may clarify the nature of minihalos.

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Paul Giles

Investigating Galaxy Clusters Utilising the Latest XCS & DES Data

Presenters: Paul Giles, University of Sussex & Tom McClintock, University of Arizona

Session: Samples and Scaling Relations II
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         The XMM Cluster Survey (XCS) has analysed the entire XMM public archive with the primary aim of producing a large catalogue of X-ray selected clusters. To date, over 5,000 extended sources have been identified as clusters of galaxies. Most of those have associated redshift and X-ray temperature information. In this presentation we will preview the second XCS data release and utilise recent DES data to describe a series of recent science results that include: the evolution and interpretation of various scaling relations (optical richness to T_x; L_x - T_x; M_x - T_x; velocity dispersion - T_x; M_lens - T_x; Y_sz - T_x); the evolution of the red sequence; constraints on modified gravity models. The presentation will feature several joint XCS-DES (Dark Energy Survey) results.

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Paul Giles

The Luminosity-velocity dispersion relation of clusters & groups detected in the XXL & GAMA surveys

Presenter: Paul Giles, University of Sussex

Session: Poster
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         The XXL Survey is the largest homogeneous survey carried out with XMM-Newton. Covering an area of 50 deg^2, the survey contains several hundred galaxy clusters out to a redshift of 2 above an X-ray flux limit of 5x10^15 erg cm^2 s^-11. The GAMA spectroscopic survey of 300000 galaxies covers 286deg^2 down to an r-band magnitude of r<19.8 mag. The overlap of these twosurveys represents an ideal opportunity to study galaxy clusters selected via two independent selection criteria. We compare the L-v relation derived from X-ray selected clusters, taking fully into account selection effects, to the relation derived from a sample of spectroscopically selected galaxy clusters from the GAMA survey. We also investigate the nature of groups detected in GAMA with a lack of X-ray emitting gas.

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Forrest Glines

Simulations of Thermal Heating from Active Galactic Nuclei

Presenter: Forrest Glines, Michigan State University

Session: Poster

Additional Authors: Brian O'Shea, Mark Voit
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         Observations from the last decade have revealed the existence of cool-core clusters, galaxy clusters with a cooling time much shorter than the dynamical time. Recent work suggests that clusters may be thermally stable due a central heating mechanism such as an active galactic nucleus (AGN) that prevents cooling. Previous analytical work in one dimension has shown that thermal heating from a central AGN with a power-law radial profile, where the heating exceeds cooling at near and far radii but not in an intermediate region, may produce a stable cluster with an isentropic entropy profile in the core and an isothermal profile outside the cluster. To test this, I simulated idealized galaxy clusters using the ENZO code with thermal heating from a central AGN. Thermal heating as a function of radius was injected proportional to the radius to a fixed exponent in (-3,-2] for each run. Total thermal feedback was set equal to the total rate of cooling in the cluster. I present entropy profiles, phase plots, and heating and cooling rates versus radius and time for several simulations. Previous numerical work with thermal and kinetic feedback through a precessing jet has shown self-regulating AGN activity. However, the kinetic feedback requires too high a spatial resolution to be useful for large cosmology simulations. A model with purely thermal feedback with the same self-regulation could be incorporated into larger simulations.

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Oleg Gnedin

On the Origin of the Correlation Between Halo Mass & Its Globular Cluster System Mass

Presenter: Oleg Gnedin, University of Michigan

Session: Samples and Scaling Relations II
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         The total mass of all globular clusters in a given large galaxy, including cluster centrals, exhibits an incredibly tight linear relation with the mass of its host halo. This relation relation has been recently established by weak lensing and dynamical measurements, and has an intrinsic scatter below 0.2 dex. It allows an independent way of determining masses of giant galaxies, groups, and clusters. I will describe a simple but accurate and predictive model for the formation of globular clusters and origin of this scaling relation. The model uncovers a slight non-linearity of the relation, which describes the data even better than a linear function.

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Philipp Grete

As a matter of force -- Systematic biases in idealized turbulence simulations

Presenter: Philipp Grete, Michigan State University

Session: Poster

Additional Authors: Brian W. O'Shea, Kris Beckwith
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         Physical processes in galaxy clusters encompass a very large dynamical range in space and time, which is not accessible by direct numerical simulations.Thus, idealized subvolumes of a cluster are often used to study small scale effects including the dynamics of turbulence.These turbulent boxes require an artificial driving in order to mimic energy injection from large scale processes such as galaxy mergers.In this presentation, we show and quantify how the autocorrelation time of the driving and its normalization systematically change properties of the flow.This includes, for example, the slope of the power spectrum, energy transfer dynamics, and the correlation between density and magnetic field strength.Given that these differences introduce a systematic bias in observables such as the line of sight magnetic field, we conclude that special care needs to be taken in interpreting results of idealized simulations.

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Liyi Gu

X-ray Spectral Modeling of the ICM: Codes, Uncertainties, & Updates

Presenter: Liyi Gu, RIKEN

Session: Hitomi Results
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         Hitomi observation of the Perseus cluster has driven a revolution in plasma code modelings, revealing a number of places where current databases such as AtomDB and SPEX needed to be updated. This talk will summarize the identified issues, the known systematic uncertainties on the related sciences, the fixes applied since Hitomi, and the on-going calculations and potential updates that are needed as more high-resolution spectral data are obtained.

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Ricardo Herbonnet

Weak Lensing - Sunyaev-Zel'Dovich Scaling Relation for ~100 Clusters

Presenter: Ricardo Herbonnet, Stony Brook University

Session: Samples and Scaling Relations II
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         The galaxy cluster mass function can place strong constraints on cosmological parameters, but only if accurate scaling relations between observables and weak gravitational lensing mass estimates are available. I will present results from a sample of ~100 massive clusters, extending the mass and redshift range probed by the Canadian Cluster Comparison Project (CCCP) with new measurements from the Multi Epoch Nearby Cluster Survey (MENeaCS). We explore the impacts of many sources of systematic errors for the weak lensing analysis: shear measurements, contamination of the source sample, obscuration of the source sample, photometric redshift distributions and conversion from shear to 3D mass and find that our results are still limited by the limited sample size. Our results allow for a reliable determination of a scaling relation with the SZ observable, which could help to explain the discrepancies seen in the Planck cluster cosmology.

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Julie Hlavacek-Larrondo

New Results on the Radio, X-ray & Optical Properties of Clusters Cores

Presenter: Julie Hlavacek-Larrondo, Université de Montréal

Session: Velocities & Turbulence, Observations and Similations
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         We present new results on the radio, X-ray and optical properties of clusters cores. We first focus on novel observations of the filamentary nebula surrounding NGC 1275, the brightest cluster galaxy (BCG) in the Perseus cluster. These observations reveal for the first time the Halpha and NII velocity structure of the nebula in its entirety (~100 kpc; 4 arcmin). Rather surprisingly, the nebula appears to harbor an extremely complex and chaotic velocity structure. However, we do observe some velocity trends that correlate with X-ray structures (bubbles, shocks, trends with distance from the AGN). We also compare these measurements to recent Hitomi measurements of the X-ray gas. The talk then focuses on presenting a new statistical study of 72 BCGs on the fundamental plane of black hole activity. Our results imply that BCGs favour advection-dominated accretion flows as the origin of the X-ray emission, and their location on the plane implies that a significant fraction (~40%) must harbour ultramassive black holes with M_BH>10^10Msun.

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Julie Hlavacek-Larrondo

The Tale of 72 BCGs: Hunting Down the Most Massive Black Holes in the Universe

Presenter: Julie Hlavacek-Larrondo, Université de Montréal

Session: Special Feature
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         TBA

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Henk Hoekstra

Mass Calibration of High Redshift Clusters

Presenter: Henk Hoekstra, Leiden University

Session: Mass Profiles and Maps

Additional Authors: Tim Schrabback
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         To infer accurate cosmological parameters from current and future large area cluster surveys it is necessary to improve the determination the mass-observable relation and its evolution. Targeted weak lensing studies of clusters at intermediate redshifts have played a prominent role in recent years, but to fully exploit the available cluster samples, we need to push the measurements to higher redshift, which is challenging. Most progress has come from mosaics of HST observations, and I will present some recent results from the follow-up of SPT clusters. I will also discuss the potential of a new approach using deep high-resolution NIR imaging. A pioneering study suggests this can compete with HST observations, thus opening up the possibility to significantly improve the calibration of the mass-observable relations at z~1.

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Henk Hoekstra

Cluster Lensing with Euclid

Presenter: Henk Hoekstra, Leiden University

Session: Future Instruments
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         Thanks to its combination of large survey area and superb image quality, Euclid will transform lensing studies of galaxy clusters. It will find many strong lensing systems that can be used to probe the inner regions. Moreover it will provide an accurate calibration of scaling relations over a wide range in mass and redshift, effectively eliminating this source of uncertainty from cosmological analyses.

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Hung-Jin Huang

Intrinsic Alignment in redMaPPer Clusters

Presenter: Hung-Jin Huang, Carnegie Mellon University

Session: Poster

Additional Authors: Rachel Mandelbaum, Peter Freeman, Yen-Chi Chen, Eduardo Rozo, Eli Rykoff, Eric Baxter
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         The observed shapes of galaxies are not randomly oriented, but rather exhibit coherent alignments with respect to the surrounding large-scale structures. In this work, we focus on studying such intrinsic alignment at one-halo scale based on a sample of ~ 80,000 member galaxies in ~ 8000 redMaPPer clusters at redshift 0.1~0.35 constructed from the Sloan Digital Sky Survey (SDSS). Two categories of alignment effects are investigated: 1) the alignment of central galaxies with the overall distribution of satellite galaxies 2) the radial alignment of satellite galaxies pointing toward cluster center. We detect alignment signals in three different shape measurement methods: re-Gaussianization, de Vaucouleurs, and isophotal shapes; discuss the impact of noise, systematics and physical effects on the detected signals. Multidimensional linear regression technique is applied to study the correlations of both types of alignment signals with a total of 17 galaxy- and cluster-related properties. We identify important predictors on the alignment effects, and discuss possible physical origins that cause the connections between the alignment signals and these identified predictors.

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Yuto Ichinohe

Atmospheric Gas Dynamics in the Perseus Cluster Observed with Hitomi

Presenter: Yuto Ichinohe, Tokyo Metropolitan University

Session: Hitomi Results

Additional Authors: Hitomi collaboration
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         We present the results associated with atmospheric gas motions within the central 100 kpc of the Perseus cluster observed with Hitomi. We find that the line-of-sight velocity dispersion of the hot gas is remarkably low and mostly uniform. The velocity dispersion reaches maxima of approximately 200 km/s toward the central active galactic nucleus (AGN) and toward the AGN inflated north-western 'ghost' bubble. Elsewhere within the observed region, the velocity dispersion appears constant around 100 km/s. We also detect a velocity gradient with a 100 km/s amplitude across the cluster core, consistent with large-scale sloshing of the core gas. If the observed gas motions are isotropic, the kinetic pressure support is less than 10% of the thermal pressure support in the cluster core. The well-resolved optically thin emission lines have Gaussian shapes, indicating that the turbulent driving scale is likely below 100 kpc, which is consistent with the size of the AGN jet inflated bubbles. We also report the first measurement of the ion temperature in the intracluster medium, which we find to be consistent with the electron temperature.

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Melanie Johnston-Hollitt

Observations of Clusters with the MWA: Uncovering Old Radio Plasma in Clusters

Presenter: Melanie Johnston-Hollitt, ICRAR-Curtin & Peripety Scientific Ltd.

Session: Nonthermal Phenomena I

         I will present the results of a systematic low frequency (70 - 230 MHz) survey of 5400 galaxy clusters using the Murchison Widefield Array (MWA). Results include the detection of large numbers of new, steep spectral index sources including new haloes, relics and 'dead' radio galaxy detections. I will discuss the importance of this newly detected population of sources with respect to the relevant cluster physics.

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Melanie Johnston-Hollitt

Future Prospects for Cluster Science with SKA & its Precursors

Presenter: Melanie Johnston-Hollitt, ICRAR-Curtin & Peripety Scientific Ltd.

Session: Future Instruments

         The next few years provides an unparalleled opportunity for radio observations of galaxy clusters with both new instruments coming online (ASKAP, MeerKAT) or existing instruments being significantly upgraded (MWA, uGMRT, LOFAR 2.0). This provides a wealth of opportunities to study objects across the radio band from tens of MHz to a few GHz with a variety of complementary telescopes capable of both high resolution imaging, and detection of diffuse, low surface brightness emission. Ultimately these efforts will culminate with Early Science on the SKA which is scheduled for 2022. I will discuss the prospects for radio observations of clusters with this new suite of instruments and describe the current timeline for science with the SKA and its precursors: MWA, ASKAP & MeerKAT.

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Christine Jones

High Redshift Galaxies Lensed by Planck Clusters

Presenter: Christine Jones, SAO CfA

Session: Galaxies in and Behind Clusters

Additional Authors: D. Coe, B. Salmon, M. Bradac et al
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         We present early results on HST lensing observations of Planck selected clusters from the RELICS project. Massive foreground galaxy clusters can magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present the z ~ 6 - 8 (plus 1 at z~10) candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ~200 arcmin^2. Although we identify 321 candidate galaxies with photometric redshifts between z ~ 6 to z ~ 8, this talk will focus on the candidates lensed by Planck selected clusters. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories.

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Tom Jones

Towards Simulating the Generation & Evolution of Cluster-Scale Turbulence & Magnetic Fields

Presenter: Tom Jones, University of Minnesota

Session: ICM Microphysics: Observations and Theory
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         ICM turbulence generated through accretion flows and mergers has important consequences for many physical properties of clusters. Among those are the strength and distribution of ICM magnetic fields, which, in turn, for example, impact key transport and dissipation properties of the ICM itself. Computational tools are now beginning to reliably reveal important properties, relationships and consequences of these processes. I will outline recent results from cosmological and supporting simulations that are helping to build clearer pictures of the dynamics and energetics behind the generation and evolution of these key ICM components.

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Ruta Kale

The Ugraded GMRT: Opening New Windows on the Radio Universe

Presenter: Ruta Kale, National Centre for Radio Astrophysics, TIFR

Session: Future Instruments

Additional Authors: Y. Gupta
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         The Giant Metrewave Radio Telescope (GMRT) is a front line international facility for low-frequency radio astronomythat has been operational for the past 15 years. It has been crucial in several exciting science areas and especiallythe impact on the studies of non-thermal radio emission from galaxy clusters has been profound. Currently a majorupgrade of the GMRT is under way that involves: i) a near seamless frequency coverage from 50 - 1500 MHz, ii) maximuminstantaneous bandwidth of 400 MHz, iii) modern servo systems, iv) sophisticated monitor and control system, andv) matching improvements in electrical and civil infrastructure. The operations of the upgrade have been carriedout while maintaining the regular legacy GMRT observations and presently three bands after the upgrade have been alreadyreleased for observations. I will present early results from the uGMRT.

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Ruta Kale

On Radio Relics in Low Mass Clusters

Presenter: Ruta Kale, National Centre for Radio Astrophysics, TIFR

Session: Nonthermal Phenomena I
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         The intra-cluster medium (ICM) in galaxy clusters is a complex plasma composed of thermal and non-thermal components. The (re)acceleration of cosmic rays at merger shocks and revival of radio lobes by shock compression are phenomena that manifest at low radio frequency bands in the form of distinct types of radio relics. Whether the cluster merger initial conditions or the cluster total masses or the availability of seed electrons decide the properties of the shock relics is still a matter of investigation. I will describe discoveries of radio relics in two low mass merging clusters that provide further clues and raise questions regarding our understanding of the generation of radio relics. I will also discuss our recent uGMRT measurements of spectral curvature in a radio relic that we are using to study the state of relativistic plasma and magnetic fields in ICM.

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Matthew Kirby

The scatter in cluster scaling relations with a complete cluster sample

Presenter: Matthew Kirby, University of Arizona

Session: Poster
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         We measure the scatter in the richness-mass relation for the 30 richest clusters in the redMaPPer catalog for the Sloan Digital Sky Survey (SDSS) using gas mass measurements from the Chandra Xray Observatory. As part of our analysis, we test for the consistency of the mass calibration of the SDSS redMaPPer and Weighing the Giants mass cluster samples. Our results provide the first direct estimate of the scatter in mass of a complete sample of redMaPPer clusters.

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Alexander Kolodzig

Hidden treasures in the noise: studying the faint end of galaxy clusters via X-ray surface brightness fluctuations

Presenter: Alexander Kolodzig, Max-Planck Institute for Astrophysics, Garching

Session: Poster

         Conventional studies of resolved clusters and groups of galaxies are strongly biased towards bright sources (i.e. massive and nearby), leading to the current poor observational constraints towards earlier structure formation phases, represented by a smaller mass or/and higher redshift of clusters. Surface brightness fluctuations of the cosmic X-ray background (CXB) carry information for the entire population, from bright, faint to even unresolved clusters. The latter represents the least massive and most distance source population, which still emits detectable X-ray photons and are inaccessible by conventional studies based on X-ray-resolved sources. I demonstrate that we are able to study this population in an unique way via angular correlation studies of CXB fluctuations with current and future X-ray surveys (e.g. XXL, Stripe 82X, SRG/eROSITA all-sky survey). For this I present the results of our pilot study based on the largest continuous Chandra survey XBOOTES (9deg^2), where we measured the most accurate power spectrum of CXB fluctuations below angular scales of ~3deg to date. After masking out resolved sources and subtracting the fluctuation signal of unresolved point sources (AGN and galaxies) from the total power spectrum, we measured a significant clustering signal from unresolved clusters. Its energy spectrum is well described by the redshifted emission spectrum of optically-thin plasma with the best-fit temperature of T~1.3keV and the best-fit redshift of z~0.4. These numbers are in good agreement with theoretical expectations based on the X-ray luminosity function and scaling relations of clusters and suggest a typical mass and luminosity of M_500 ~ 10^13.6 M_Sun/h and L_(0.5-2.0keV) ~ 10^42.5 erg/s, respectively, of the unresolved cluster population. The energy spectrum of the fluctuation signal of resolved clusters shows a much higher temperature (T~2.1keV) and lower redshift (z~0.2), agreeing with theoretical expectations. We show that the power spectrum shape is sensitive to the structure of the intracluster medium (ICM) of a cluster all the way to the outskirts, out to a ~few R_500, outperforming conventional studies by factor of ~2-3. We also searched for possible contribution of the warm-hot intergalactic medium (WHIM) to the observed CXB fluctuations.

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Andrey Kravtsov

Splashback as a Physical Boundary of Halos

Presenter: Andrey Kravtsov, The University of Chicago

Session: Mass Profiles and Maps
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         I will briefly discuss the standard definitions of halo mass and some issues with interpretation of scaling relations that use such mass definitions.I will argue that density caustic formed by particles that orbited through halo once and just reached their apocenter -- called the splashback shell - can be conisdered as a natural physical boundary of halos. Such caustics are predicted by analytic model of peak collapse and have now been convincingly showedto exist around real halos formed in cosmological simulations, as well as around real observed clusters. I will review methods to identify splashback shells in simulations and will present a number of properties of such shells and their dependence on halo properties. In particular I will present measurements of the extent of the splashback shell and its dependence on halo mass accretion rate. I will also review recent detections of splashback in observations and implications for galaxy evolution and environmental effects.

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Andrey Kravtsov

Lynx & Clusters

Presenter: Andrey Kravtsov, The University of Chicago

Session: Future Instruments
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         No Abstract

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Matthew Kunz

Things Fall Apart: Waves & Turbulence in a Weakly Collisional ICM

Presenter: Matthew Kunz, Princeton University

Session: ICM Microphysics: Observations and Theory
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         I will discuss what microphysical constraints are imposed on waves and turbulence in a weakly collisional, high-beta plasma such as the intracluster medium, as well as how such a plasma copes with these constraints. [abridged]

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Amandine Le Brun

Internal Dark Matter Structure of the Most Massive Galaxy Clusters Since Redshift 1

Presenter: Amandine Le Brun, Département d'Astrophysique CEA Saclay

Session: Mass Profiles and Maps

Additional Authors: Monique Arnaud, Gabriel W. Pratt, Romain Teyssier

         The evolution of the dark matter profiles of high-mass galaxy clusters from z~1 to the present day remains poorly constrained and is a powerful test of the LambdaCDM model. Such a test requires systematic confrontations of observations of a representative sample of the Universe's most massive clusters, preferably in several redshift bins, with tailor-made numerical simulations. To date, there exist no cosmological numerical simulations with the exceptionally large volume (required to simulate the rarest, most massive clusters) and the resolution (required to resolve their structure) necessary to undertake such a project. We will present the first results from a simulation campaign aimed at producing large cosmological simulations that are 1 Gpc/h on a side and have a medium mass and spatial resolution. They are being complemented with very-high resolution zoom simulations which are progressively including the non-gravitational physics of galaxy formation such as star formation, supernova and AGN feedback. The simulations are produced using the AMR code RAMSES. The first results are based on a subset of the systems, consisting of the 25 most massive galaxy clusters at each redshift (z=1, 0.8, 0.6 and 0) to study the evolution of their internal structure, finding that their dark matter profiles within r500 are strikingly similar from z ∼ 1 to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, but their inner structure shows no signs of converging to an asymptotic slope. This suggests that this type of profile is already in place at z > 1 in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.

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Guillaume Mahler

Strong-lensing analysis of Abell 2744 with MUSE & Hubble Frontier Fields images

Presenter: Guillaume Mahler, University of Michigan

Session: Poster
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         I will present an analysis of the mass distribution of the galaxy cluster Abell 2744. This cluster was targeted by the Hubble Frontier Fields program specifically for its massive core, which induces a large strong lensing effect.I used the observation made by the MUSE spectrograph on VLT designed to construct a 2’x2’ IFU mosaic covering the entire multiply imaged region with a typical exposure time of ~6h.This new dataset enable to discover 514 redshifts (414 new) including 156 galaxy cluster members, more than 200 background galaxies, and confirmed 83 multiple images associated with 29 systems. It appears that the cluster members in the inner core reproduce the large scale structure previously discovered. In addition, the large fraction of spectroscopically confirmed lensed images (83 out of 188) make this cluster one of the most constraint clusters to date. The mass models of the cluster core is now sensitive enough to be able to distinguish between simple models taking care of the outskirts mass influence to the core.The analysis of the systematic uncertainties on this mass model brings useful information of having a large number of spectroscopic constraints and their effect on the mass distribution and the magnification of the cluster.

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Soumyajit Mandal

Ultra Steep Spectrum Sources in Galaxy Clusters: Mechanisms for Particle (Re)-acceleration

Presenter: Soumyajit Mandal, Leiden University

Session: Poster
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         Low-frequency radio observations have revealed the presence of large-scale synchrotron emitting sources in galaxy clusters. Over the last decade is has become clear that these sources trace particles (re-)accelerated by shocks and turbulence generated during major merger events. However, the physics of these particle acceleration processes is still poorly understood. One of the main open questions is the fate of fossil relativistic electrons deposited in the intra-cluster medium, e.g., the lobes and tails of cluster radio galaxies. Are these fossil electrons re-accelerated by merger-induced shocks and turbulence? And is there a link to the generation of giant radio halos and relics? We have carried out GMRT follow-up observations of a unique sample of diffuse, ultra-steep-spectrum radio sources in galaxy clusters selected from the GMRT 150-MHz sky survey (TGSS) and follow-up LOFAR, Chandra observations are underway. By determining their detailed properties, we aim to establish the origin of these sources, as well as their connection to ICM particle re-acceleration processes.

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Maxim Markevitch

Shock Front Physics & New Subtle X-ray Features in Clusters

Presenter: Maxim Markevitch, NASA GSFC

Session: ICM Microphysics: Observations and Theory

Additional Authors: Qian Wang
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         I will present a constraint on the electron-ion equilibration timescale in the ICM from the prominent shock front in the merging cluster A520. Several examples of a newly discovered phenomenon -- subtle long channels in the X-ray gas of some merging clusters -- will also be presented. It is possible that they arise because of plasma depletion in regions of the ICM where the magnetic field is strongly amplified. I will also present a search for spatial correlation between the X-ray and radio brightness in the bright radio relic of A3667, which may provide be evidence for inverse Compton emission.

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Maxim Markevitch

AXIS - Advanced X-ray Imaging Satellite, a NASA Probe Under Study

Presenter: Maxim Markevitch, NASA GSFC

Session: Future Instruments

Additional Authors: R. Mushotzky, W. Zhang, A. Ptak, A. Fabian, et al.
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         Advanced X-ray Imaging Satellite, or AXIS, is one of the possible probe-class missions for the 2020s, currently under NASA study. It is essentially a super-Chandra, with 0.3" angular resolution across a broad field of view, a 0.3-10 keV energy band with 10 times the Chandra effective area at E=1 keV, a CCD or active-pixel detector, launched into a low-Earth orbit. While the main science drivers are compact sources, several cluster science topics will be advanced dramatically by such a mission. They include resolving the Bondi radii around the cluster central AGN utilizing the high angular resolution, and mapping the cluster emission beyond the virial radii and into the WHIM, taking advantage of the very low relative detector background and the completely resolved extragalactic CXB.

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Pasquale Mazzotta

Enlighten the Structure of the Cluster Outskirts with SZ & X-ray Observations

Presenter: Pasquale Mazzotta, Dipartimento di Fisica Universita' di Roma "Tor Vergata"

Session: Cluster Outskirts

Additional Authors: Herve' Boudin, Elena Rasia, Anna Silvia Baldi , Arpine Kozmanyan
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         The Sunyaev-Zeldovich (SZ) effect is excellent to detect the presence of hot gas out to the galaxy cluster peripheries.Using a newly developed technique to extract the SZ signal from microwave frequency maps, we present the results of some projects devoted to the detailed study of the outskirts of clusters of galaxies up to z~1 obtained by combining Planck and X-ray observations.

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Tom McClintock

Cosmological Constraints from the DES Y1 redMaPPer Cluster Sample

Presenter: Tom McClintock, University of Arizona

Session: Poster

         I will present cosmological constraints derived from volume-limited samples redMaPPer clusters in the DES Year 1 and SDSS data sets. The clusters have precisely quantified photometric redshifts and centering properties. We account for systematics such as membership dilution of the lensing source galaxy population, projection effects that alter both the lensing and richness measurements, and biases inherent to our fitting procedure, as quantified using numerical simulations. In addition, I will present a halo mass function emulator capable of predicting the halo mass function in arbitrary flat wCDM cosmologies with 1% precision. This factor of five improvement relative to the previous state-of-the-art models will render this source of systematic uncertainty negligible in the era of LSST, Euclid, and WFIRST.

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Michael McDonald

Revisiting the Cooling Flow Problem in Galaxies, Groups, & Clusters

Presenter: Michael McDonald, MIT

Session: Cool Cores I: Statistics, Formation and Destruction

Additional Authors: Massimo Gaspari, Brian McNamara, Grant Tremblay

         In the past decade, significant progress has been made towards resolving the cooling flow problem. However, while much effort has focused on understanding the solution, relatively little recent work has focused on the problem. I will present a recent work in which we combine new estimates of the classical ICM cooling rate with reliable estimates of the star formation rate for 107 clusters, spanning 3 orders of magnitude in mass, 5 orders of magnitude in star formation, 4 orders of magnitude in cooling rate, and 5 orders of magnitude in black hole accretion rate. Using these data, we are able to constrain the slope and scatter of the SFR-dM/dt relation, finding that it is well fit with a broken power law (SFR uncorrelated w/ cooling rate at low-mass, strongly correlated at high-mass) with large (~0.5 dex) intrinsic scatter. We will discuss the implication of these results, which have laid the groundwork for a larger, upcoming survey extending to z>1.

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Brian McNamara

ALMA's Perspective on Fueling Feedback in Massive Galaxies

Presenter: Brian McNamara, University of Waterloo

Session: Cool Cores III: Rain and Fountains

Additional Authors: Helen Russell
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         TBD

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Elinor Medezinski

Weighing Galaxy Clusters with Weak Lensing in Hyper Suprime-Cam Survey

Presenter: Elinor Medezinski, Princeton University

Session: Mass Profiles and Maps

Additional Authors: HSC collaboration
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         In order for cluster abundance to reach its full potential as the next precision cosmology tool, accurate cluster masses are a key. Weak lensing provides the best direct probe of the total cluster mass, but it requires high-quality wide-field imaging and better control of systematics. With its unprecedentedly deep and exquisite seeing, the Subaru Hyper Suprime-Cam (HSC) survey is an ongoing campaign to observe 1,400 square degrees to r~26, providing the best current precursor for LSST. In this talk, I will present our new field-leading results from the first HSC data release of ~150 square degrees that encompass thousands of clusters. Harnessing our new HSC survey, I measure benchmark weak lensing cluster masses with improved methodology, and reconcile previous tension on cosmological parameters between the SZ and CMB within the Planck survey.

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François Mernier

Spatial Distribution of Metals in the Intracluster Medium

Presenter: François Mernier, MTA-Eötvös University Lendület

Session: Abundances
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         The hot intracluster medium (ICM) permeating galaxy clusters and groups is continuously enriched by metals, all synthesized in stars and supernova explosions. While O, Ne, and Mg are produced almost exclusively by core-collapse supernovae (SNcc), heavier elements like Ca, Cr, Fe, and Ni are mostly synthesized when white dwarfs explode as Type Ia supernovae (SNIa). Intermediate elements like Si, S, and Ar are produced by both SNcc and SNIa in comparable amounts. The spatial distribution of all these elements - which has been possible to constrain over the last decades thanks to the most recent generations of X-ray observatories - constitute a remarkable signature of the chemical history of galaxy clusters throughout cosmic time. Therefore, measuring accurately the elemental abundances from the core to the outskirts of clusters helps us to understand: (i) when and how was the ICM enriched, (ii) the possible differences between SNIa and SNcc contributions at cluster scales, and (iii) how do stellar and AGN feedback affect the formation, growth, and chemical enrichment of clusters.Among other results from the recent literature, in this talk we present and discuss the best constrained average radial profiles of O, Mg, Si, S, Ar, Ca, Fe, and Ni obtained to date, based on the XMM-Newton observations of 44 cool-core clusters, groups, and elliptical galaxies (the CHEERS sample).

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Nceba Mhlahlo

A Suspected Shock Front in the Merging Cluster of Galaxies ACO2163

Presenter: Nceba Mhlahlo, University of the Witwatersrand

Session: Poster
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         ACO2163 is one of the hottest Abell galaxy clusters which has been observed countless times through different wavelengths and has always shown remarkable properties. We report on a detection of a suspected shock front in ACO2163 through the use of XMM-Newton X-ray observations which were combined with the radio observations to determine the shock location in relation to the radio emission and other specific parameters inherent to the shock front. We extracted X-ray spectra to determine the luminosity and temperature in the area around the edge of the cluster. From a temperature jump we obtain a Mach number of 2.2±0.3, which is a typical value for shocks in merging galaxy clusters. The radio study has been conducted using VLA data where we have done a spectral analysis of the radio halo region. We find that the south-western region of the cluster where the shock is located is globally flat, indicating the presence of energised electrons in this region.

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Rogério Monteiro-Oliveira

Unveiling the dark side of the Universe through the merging galaxy clusters

Presenter: Rogério Monteiro-Oliveira, University of São Paulo

Session: Poster

Additional Authors: Eduardo S. Cypriano, Rubens E. G. Machado & Gastão B. Lima Neto
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         The merger of galaxy clusters consists of an excellent astrophysical laboratory for the study of their three main components: dark matter (DM), intra-cluster medium gas (ICM) and galaxies. The main feature for the investigation about the self-interacting behaviour of the DM comes from the observed detachment between the cluster DM halo and the ICM distribution observed soon after the pericentric passage. A question is: what the conditions for the occurrence of such detachments? In this talk, we will present some insights regarding this topic based on a combined mass reconstruction plus hydrodynamical simulation of the merging galaxy clusters Abell 1758 (z = 0.27) and Abell 3376 (z = 0.046), both consisting on double systems (main cluster and subcluster). Whereas in A1758 the main (and most massive) cluster has retained its gas content (i.e. no detachment is observed), in A3376 this happened in the less massive substructure, showing that the mass alone cannot explain the detachment observed in dissociative systems. On the other side, our simulations suggest that the gas concentration take an important role on that.

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Tony Mroczkowski

SZ Instruments at High Resolution

Presenter: Tony Mroczkowski, ESO

Session: Future Instruments
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         I will attempt to provide a general overview of current and near future instrumentation at 30-400 GHz capable of probing the thermal and kinetic Sunyaev-Zel'dovich effects at subarcminute resolution. This includes current and planned instrumentation for the Atacama Large Millimeter/Submillimeter Array (ALMA), the 100-meter Green Bank Telescope (GBT), the IRAM 30-meter telescope, the 50-meter Large Millimeter Telescope, and potential new projects like the approximately 40-meter Atacama Large Aperture Submillimeter/Millimeter Telescope (AtLAST), the 50-meter Large Submillimeter Telescope (LST) led by NAOJ, the 30-meter Chajnantor Sub/mm Survey Telescope (CSST), and the originally-planned 25-meter CCAT. This talk is meant to complement planned talks given by specific instrumentation groups, and will hopefully serve as an objective comparison. A strong caveat is that predictions for future instrument performance are difficult, particularly since ground-based observations at mm/submm wavelengths are sensitive to reliability of atmospheric subtraction.

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Daisuke Nagai

Modeling Challenges for Cluster Astrophysics in the Era of Multi-Wavelength Cosmology

Presenter: Daisuke Nagai, Yale University

Session: Advances in Simulations
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         Upcoming multi-wavelength cosmological surveys promise to provide a vastly broaden view of the formation and evolution of galaxy clusters and large-scale structure (LSS) of the universe. However, making sense of these new observations will require development of a computationally efficient and physically motivated theoretical models to enable joint analysis of data from the same sky. In this talk, I will present such a model and its application for interpreting data obtained by the current generation of LSS and CMB surveys, including cross-correlation studies of thermal SZ effect and weak lensing and kinematic SZ effect as probes of cosmology and astrophysics.

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A. Nagarajan, Kaustuv Basu

Weak-lensing Mass Calibration of the Sunyaev-Zel'dovich Effect Using APEX-SZ Galaxy Clusters

Presenter: Kaustuv Basu, University of Bonn (Lead author: A. Nagarajan)

Session: Poster

         The use of galaxy clusters as precision cosmological probes relies on accurate determination of their masses. However, inferring the relationship between cluster mass and observables from direct observations is difficult and requires adequate control of the systematic effects caused by sample selection. In this work, we present results on the mass calibration of the integrated Comptonization using weak-lensing estimates for an X-ray selected complete sample. A special focus was placed on the role played by the intrinsic covariance between the X-ray luminosity and the integrated Comptonization at fixed mass. Our constraints on the correlation between the intrinsic scatters of the cluster observables favour a positive value. Ignoring this correlation tends to bias the Comptonization-mass relation, even though the Comptonization played no role in the sample selection. We study the impact of such systematic biases in scaling relations on some near-future cluster-based cosmological experiments and find that the systematic effect could dominate the cosmological error budget.

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Shinya Nakashima

Temperature Structure in the Perseus Cluster Core Observed with Hitomi

Presenter: Shinya Nakashima, RIKEN

Session: Hitomi Results
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         I will present the Hitomi observational result of the temperature structure in the Perseus cluster core.The Soft X-ray Spectrometer aboard Hitomi resolved many emission liens that are degenerated in previous CCD measurements, and enable us to perform the precise line ratio diagnostic of the hot intracluster medium. We found that the observed temperature structure is consistent with the prediction from the projection effect and no higher temperature components (>8 keV) are seen in the Hitomi spectrum. Signature of the non-ionization-equilibrium state is also not found. In contrast to the complex spatial structure, quiescent view of the hot intracluster medium is shown from the Hitomi observation.

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Allison Noble

An ALMA Study of Gas-Rich Galaxies in z~1.6 Galaxy Clusters

Presenter: Allison Noble, Massachusetts Institute of Technology

Session: Galaxies in and Behind Clusters

Additional Authors: M. McDonald, A. Muzzin, J. Nantais, G. Rudnick, E. van Kampen, T. M. A. Webb, G. Wilson, H. K. C. Yen, et al.
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         Galaxy cluster evolution is intertwined with that of its constituent galaxies. Therefore in order to understand the former, we must also explore the baryonic processes the shape the latter. In particular, this requires a solid understanding of the evolution of the molecular gas content in cluster galaxies, since the gas provides the necessary raw material to feed star formation. I will present ALMA CO 2-1 detections in eleven cluster galaxies at z~1.6, in one of the largest studies of molecular gas in high-redshift clusters to date. These cluster galaxies have main-sequence star formation rates but gas fractions up to 60-80%. In the local universe, high-density clusters are devoid of star-forming gas-rich galaxies; with these ALMA data, we are witnessing the first direct evidence that gas-rich galaxies are located indistinguishably in both the field and clusters at high redshift.

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Gaël Noirot

Star Formation Activity in Confirmed Clusters and Proto-Clusters at 1.4 < z < 2.8.

Presenter: Gaël Noirot, JPL

Session: Poster

Additional Authors: Daniel Stern, Simona Mei, Dominika Wylezalek, Elizabeth A.Cooke, Carlos De Breuck, Audrey Galametz, Nina A.Hatch, Joel Vernet, Mark Brodwin, Peter Eisenhardt, Anthony H.Gonzalez, Matt Jarvis, Alessandro Rettura, Nick Seymour, S.A.Stanford
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         Radio-loud AGN (RLAGN) tend to reside in the most massive dark matter halos, and have a long history of being used to efficiently identify rich, high-redshift structures (i.e., clusters and proto-clusters). Our team led the “Clusters Around Radio-Loud AGN” (CARLA) survey, which was a 400-hr Spitzer program surveying 420 RLAGN (radio-loud quasars and high-redshift radio galaxies) at 1.3 < z < 3.2 across the full sky. CARLA identified 200 cluster candidates as significant overdensities of red color-selected Spitzer/IRAC galaxies around the RLAGN. I will present results from our follow-up 40-orbit Hubble Space Telescope program of the 20 densest CARLA cluster candidates. We spectroscopically confirm 16 of the 20 distant structures associated with the RLAGN, out to z=2.8 (Noirot et al. 2016, 2018). For the first time at these redshifts, we statistically investigate the star-formation content and line-ratios of a large sample of galaxies in dense structures. I will show that 1.4 < z < 2.0 massive member galaxies form fewer stars than their field counterparts, consistent with an accelerated evolution in dense environments already at these epochs. I will also show that at 1.4 < z < 2.0, CARLA cores are the main sites of star formation, consistent with the onset of the reversal in the star formation rate - density relation at z ~ 1.4. This survey represents a unique and large homogenous sample of spectroscopically confirmed structures at high redshifts, ideal to further study galaxy cluster physics, star-formation, quenching mechanisms, and AGN feedback. CARLA samples the previously largely unexplored transition epoch between proto-cluster and cluster environments.

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Chris Nolting

Shocked Radio Galaxy Jets: Clues To Cluster Weather

Presenter: Chris Nolting, University of Minnesota

Session: ICM Microphysics: Observations and Theory

Additional Authors: Tom Jones
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         Intracluster medium dynamics remain difficult to ascertain directly, but with the abundance of radio galaxies in clusters, we can gain insight into the ICM motions that cause distortions in radio galaxy jets and the cavities they create. A series of MHD simulations of AGN jets interacting with cluster merger shocks is discussed. Energy dependent relativistic cosmic ray electron transport allows for realistic synthetic radio observations of non-thermal synchrotron emission and more direct comparison to observed radio images.

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Paul Nulsen

Cygnus A: a Powerful Radio Galaxy in a Cool Core Cluster

Presenter: Paul Nulsen, Harvard-Snithsonian Center for Astrophysics

Session: Cool Cores II: heating vs. cooling

Additional Authors: Bradford Snios, Michael Wise, Martijn de Vries, Mark Birkinshaw, Diana Worrall, Ryan Duffy, Ralph Kraft, Brian McNamara, Chris Carilli, Juidth Croston, Alastair Edge, Leith Godfrey, Martin Hardcastle, Daniel Harris, Robert Laing, William Mathews, John McK
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         The nearest truly powerful radio galaxy, Cygnus A, is hosted by the central galaxy of a cool core cluster. The gas rich environment enables the radio outburst to be studied in detail in the X-ray. I will report results obtained from 2 Msec of Chandra X-ray data for Cygnus A, focusing on the properties of its cocoon shocks and what they tell us about the outburst. While the shock strength varies around the cocoon, the postshock pressure is relatively uniform, reflecting the pressures within the radio lobes. The mean power deposited by the jets approaches 10^{46} erg/sec over the 20 Myr duration of the outburst. Estimates of the jet power and cocoon pressure can be used together with the properties of the hotspots of this Fanaroff-Riley class II radio source to model the properties of its jets. Our results favor models in which the power and momentum of the jets are carried primarily in the internal energy of the jet plasma rather than in rest mass, i.e. light jet models.

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Anna Ogorzalek

Using New Hot Gas Velocity Measurements To Probe Feedback in Massive Galaxies

Presenter: Anna Ogorzalek, KIPAC/Stanford

Session: Cool Cores II: heating vs. cooling

Additional Authors: I. Zhuravleva (Stanford), S. W. Allen (Stanford), C. Pinto (Cambridge), N. Werner (MTA-Eotvos University), A. B. Mantz (Stanford), R. E. A. Canning (Stanford), A. C. Fabian (Cambridge), J. S. Kaastra (SRON), J. de Plaa (SRON)
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         Velocity structure of X-ray emitting atmospheres of massive galaxies and galaxy cluster cores remains a key open question in our understanding of galaxy formation and mechanical AGN feedback. Bringing together resonant scattering and direct line broadening techniques applied to deep XMM-Newton Reflection Grating Spectrometer observations has allowed us for the first time to measure turbulent velocities in the cores of 13 nearby giant elliptical galaxies, and therefore look at typical properties of hot gas motions in such objects. Our method has also been successfully applied to the Hitomi Perseus observation, serving as an independent velocity probe. In this talk I will introduce our measurements and their implications on the physics of kinetic AGN feedback. I will also discuss the role of resonant scattering in studying gas dynamics of cooler systems, such as e.g. group-central galaxies, and emphasize its importance for correctly interpreting high resolution X-ray spectra from XARM and ATHENA.

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Florian Pacaud

The SXG/eROSITA All-Sky Survey

Presenter: Florian Pacaud, AIfA - University of Bonn

Session: Future Instruments

Additional Authors: for the eROSITA collaboration

         eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian-German Spectrum-Roentgen-Gamma (SRG) mission, which is currently scheduled for launch in late 2018. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of a large (10^5) sample of galaxy clusters up to redshifts z > 1 in order to study the large-scale structure in the universe and test cosmological models, including dark energy. In addition, eROSITA is expected to yield a sample of a few million active galactic nuclei and provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the galaxy.

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Florian Pacaud

Galaxy Clusters in the XXL Survey

Presenter: Florian Pacaud, AIfA - University of Bonn

Session: Samples and Scaling Relations II

Additional Authors: for the XXL collaboration

         The XXL survey covers two 25deg2 patches with XMM observations of ~10ks. It is currently the widest contiguous medium-deep X-ray survey ever performed. In this contribution, I will present the scientific results related to galaxy clusters associated with the first (mid-2016) and second (upcomming) releases of the XXL dataset. This includes (among other things) galaxy cluster scaling relation studies, baryon content estimate and early cosmological results. I will also discuss the prospects for improving the cluster mass calibration and their impact on XXL cosmological results. With its exquisite associated multi-wavelength dataset, XXL will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA, Euclid and LSST missions.

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Prakriti Palchoudhury

Multiphase gas in the circumgalactic medium: role of t_cool /t_ff & δρ/ρ

Presenter: Prakriti Palchoudhury, Indian Institute of Science, Bengaluru, India

Session: Poster

Additional Authors: Prateek Sharma
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         Galaxy formation in dark matter haloes is understood to be a conse-quence of the combined effects of cooling, heating, and gravity. Gas doesnot simply cool out of the hot, virialized intracluster medium (ICM), butis maintained in rough thermal balance due to energy input by activegalactic nucleus (AGN) jets in cores of galaxy clusters. Simulations inspherical atmospheres as well as some observations show that cold gascondenses out of the ICM for a ratio of cooling time to the free-fall timeless than a threshold value close to 10 (i.e t_cool /t_ff <=10). Simulations in plane-parallel atmospheres, in which heating balances cooling in shells, had put the threshold to be 1, which is more intuitive. In the first part of this work we set up a linear eigen problem that solves for the growth rates of thermal instability in spherical and plane-parallel geometries, for NFW as well as idealized gravitational potentials. We find that the linear growth is independent of geometry. We validate these findings in realistic simulations with NFW and other idealized potentials. In simulations we study the non-linear growth of isobaric density perturbations and see that while t_cool /t_ff <=1 is required for in-situ condensation(which earlier plane-parallel simulations have focused on), t_cool /t_ff<=10 (within a factor of 2) holds good for condensation anywhere in the medium. This result is independent of the geometry of the atmosphere. However, with heating balancing cooling in shells, there is significant transfer of energy across layers, triggering condensation in the upper layers and driving t_cool /t_ff above 10. Triggered condensation is significant in plane-parallel geometry because of a larger volume of the central cooling region. More recently, we have explored simulations with higher density perturbations in realistic halo potentials. We find that for overdensity amplitudes less than 1, there exists a limiting min(t_cool /t_ff ) that sets the threshold for multiphase condensation. But for high density contrasts in the ICM, gas condenses outof the medium independent of the background t_cool /t_ff . We also introducea condensation curve that defines a zone of multiphase condensation inthe t_cool /t_ff -δρ/ρ space for different ICM conditions.

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Mahadev Pandge

A detailed study of AGN feedback in Abell 3016

Presenter: Mahadev Pandge, Dayanand Science College, latur, India

Session: Poster

         We present an in-depth analysis of a cool-core galaxy cluster \mac~(z=0.219), which has been identified to be merging with its companion cluster Abell~3016. This study has made use of the {\it Chandra} X-ray, ESO VLT optical and the GMRT radio archival data of this cluster. Using various image processing techniques like, 2-d beta modeling, unsharp masking, contour binning and surface brightness profiling, we detect a pair of X-ray cavities (denoted as Ecavity and Wcavity) at a projected distance of ~$\sim$ 20 arcsec (70\,kpc) and ~$\sim$16 arcsec (57\,kpc), respectively from the core of \mac. We also detect an excess X-ray emission towards the south which is at $\sim$25 arcsec (88\,kpc) from the centre and relatively hotter than that of the surroundings, indicating that an in-falling galaxy group may be responsible for the hike in temperature at this region. We find that the radio lobes are responsible for carving the observed X-ray cavities detected in this system. The lower values of mid-IR WISE colour [W1-W2] and [W2-W3] imply that the central BCG of \mac~ is a star forming galaxy. The current star formation rate of central BCG estimated from the ${\rm H\alpha}$ and {\it GALAX} FUV luminosities are equal to be $\sim 5.06\pm0.78$ \Msun yr$^{-1}$ and $\sim 9.20\pm0.81$ \Msun yr$^{-1}$, respectively.

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Rachel Paterno-Mahler

X-Ray Properties of Lensing-Selected Clusters

Presenter: Rachel Paterno-Mahler, University of California, Irvine

Session: Poster

Additional Authors: David Buote, Yuanyuan Su
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         I will present results from the Michigan Swift X-ray observations of clusters from the Sloan Giant Arcs Survey (SGAS). These clusters were lensing selected based on the presence of a giant arc visible in SDSS. I characterize the morphology of the intracluster medium (ICM) of the sample and discuss the offset between the X-ray centroid, the mass centroid as determined by strong lensing analysis, and the BCG position.

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Sanjaykumar Patil

Measuring mass of Galaxy Clusters using Cosmic Microwave Background lensing

Presenter: Sanjaykumar Patil, University of Melbourne

Session: Poster

Additional Authors: Srinivasan Raghunathan, Christian Reichardt

         Galaxy clusters are the largest gravitationally bound objects in the Universe and provide crucial insight to the standard model of Cosmology. Their abundance as a function of mass and redshift is highly sensitive to cosmological parameters such as the amplitude of matter fluctuations and the dark energy equation of state.Though galaxy clusters are powerful probes of cosmology, they are currently limited by a ~15% mass uncertainty. Future optical (LSST) and X-ray (eROSITA) surveys will provide even larger samples of galaxy clusters; our ability to fully realise the potential of these samples depends on better mass estimates. Gravitational lensing is widely considered as the gold standard in mass estimation.In this talk I will present a method to extract the lensing signal from the Cosmic Microwave Background (CMB) data. With this method we predict mass uncertainties will be improved to 3-6% for upcoming CMB experiments (SPT-3G, AdvACT etc) to less than 1% for next stage CMB experiment (CMB-S4).

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Ana Paulino-Afonso

Optical rest-frame spectroscopy to study the filaments & galaxy clusters outskirts at z~1

Presenter: Ana Paulino-Afonso, Institute of Astrophysics and Space Sciences (Portugal)

Session: Poster

Additional Authors: Dr. David Sobral, Dr. Behnam Darvish, Dr. Bruno Ribeiro, Dr. Andra Stroe and Dr. José Afonso

         The VIMOS Spectroscopic Survey of a Supercluster in the COSMOS field (VIS³COS) aims to accurately map in 3D a superstructure at redshift between 0.8 and 0.9, which contains 3 massive X-rays confirmed clusters (Finoguenov et al., 2007) and shows a striking filamentary structure in the HiZELS Hα survey at z=0.84 (Sobral et al., 2011). The ~500 spectroscopic confirmed members probe a wide range of densities and environments (from fields to the clusters outskirts and rich groups). The unprecedented nature of this survey (Paulino-Afonso et al., A&A submitted) allows a detailed study of the evolution of these objects across cosmic time as well as link observations and theories in and around cluster galaxies by e.g. characterising the star formation activity and the ionised gas properties of galaxies in a large density range. I will present the observed depression of star formation and local changes on electron densities with environment (depending on galaxy stellar mass) at z~1, where most changes occur in cluster outskirts and filament-like regions. At this epoch, the intense life in the cluster galaxies suburbs seems to provide essential clues on the physical mechanisms that can affect the shape of galaxy clusters and their understanding.

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Ana Paulino-Afonso

Mergers, shocks & turbulence & their effects on galaxy evolution

Presenter: Ana Paulino-Afonso, Institute of Astrophysics and Space Sciences (Portugal)

Session: Poster

Additional Authors: Dr. Andra Stroe

         Galaxy populations in relaxed clusters are dominated by ellipticals. However, little is known boy the effect of disturbed clusters on galaxy evolution. Merging clusters represent an extremely violent environment permeated by Mpc-wide shock waves and cluster-wide turbulence. Stroe et al. (2016) completed the first narrow-band survey of Hα emitters in a sample of low-redshift clusters sampling a range of masses and relaxation states. The results have shown that relaxed environments have 25 times fewer Hα emitters compared to merging clusters. What drives this reversal of typical environmental trends and how could shocks and turbulence trigger star formation in cluster galaxies remains unclear. Multi-object spectroscopic observations have been granted using VLT/VIMOS and WHT/AF2 in order to efficiently follow-up star formation galaxies and AGN uniformly selected in relaxed and merging clusters. This will allow us to measure the precise redshift, powering source, metallicity, electron density and ionisation parameters of these sources. Given the similarities between low-redshift disturbed clusters and high-redshift protoclusters, this unique study not only provides an excellent opportunity to connect observations and theory but it may also provide important clues to the evolution of galaxies at high-redshift analogs.

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Annalisa Pillepich

Simulating Galaxy Clusters (and Their Galaxies!) with IllustrisTNG

Presenter: Annalisa Pillepich, MPIA Heidelberg

Session: Advances in Simulations
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         I will review the efforts to simulate large volume hydrodynamical simulations with the moving-mesh code AREPO for galaxy formation and cosmological applications. In particular, I will focus on the new synthetic dataset of hundreds of massive galaxy clusters produced with the IllustrisTNG simulations and including the effects of MHD, AGN and stellar feedback, gas cooling and heating, stellar evolution and chemical enrichment, all at unprecedented resolution. I will give an overview of the insights these simulations allow us to gain, starting with the distribution and properties of their stellar, gaseous and dark-matter content.

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Etienne Pointecouteau

Cluster Results From the Planck Survey

Presenter: Etienne Pointecouteau, IRAP

Session: Samples and Scaling Relations I
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         I will review the results from the Sunyaev-Zel'dovich observations in the Planck Survey and their relevance for the study of the physics of galaxy clusters.

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Etienne Pointecouteau

Cluster Science with Athena

Presenter: Etienne Pointecouteau, IRAP

Session: Future Instruments
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         Athena is the next generation of X-ray telescope within the European Space Agency science program. I will present the science goal associated with clusters of galaxies including unveiling the first groups in the Universe, cluster assembly, evolution across cosmic time, AGN feedback in clusters, etc.

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Ana-Roxana Pop

X-ray & SZ Scaling Relations in IllustrisTNG

Presenter: Ana-Roxana Pop, Harvard University

Session: Poster

Additional Authors: collaborators include David Barnes, Lars Hernquist, Rahul Kannan, Federico Marinacci, Mark Vogelsberger and the IllustrisTNG collaboration

         We present X-ray and SZ results from an updated ensemble of numerical simulations — IllustrisTNG (The Next Generation). This new run of the Illustris simulation introduces an updated physical model to simulate the formation and evolution of galaxies in cosmological, large-scale gravity + magnetohydrodynamical simulations. One of the primary improvements to the Illustris galaxy model is related to AGN feedback. At high accretion rates relative to the Eddington limit, we continue to assume that a fraction of the accreted rest mass energy heats the surrounding gas thermally. However, for low accretion rates, we use a new, kinetic (SMBH driven wind) feedback model that imparts momentum to the surrounding gas in a stochastic manner. We will investigate how the new feedback model affects typical X-ray scaling relations (e.g., L_x vs. M_500c and M_500gas, L_x vs. mass-weighted and spectroscopic gas temperatures: T_mw and T_X) and compare the results to both observations and the original Illustris run. We also discuss the new integrated Compton Y parameter scaling relations with M_500c, M_500gas, and T_X. Finally, we compare gas density, temperature and pressure profiles for our most massive galaxies. As part of the new ensemble of numerical simulations, IllustrisTNG also includes a larger box (~300 Mpc on a side) which allows us to significantly increase our statistics for the most massive clusters in our simulation (~ 2500 objects above M_500c = 10^13 M_sun in IllustrisTNG vs. less than 100 in the 100 Mpc Illustris box, and ~150 clusters in IllustrisTNG with M_500c > 10^14 M_sun).

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Deovrat Prasad

Role of BCG & AGN-Driven Turbulence in Cool-Core Clusters

Presenter: Deovrat Prasad, Indian Institute of Science, Bangalore, India

Session: Cool Cores III: Rain and Fountains

Additional Authors: Prateek Sharma, Arif Babul
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         Cold mode AGN feedback maintains global thermal equilibrium in the intra-cluster medium (ICM) of cool-core galaxy clusters. Idealised and realistic ICM-jet simulations show that if the ratio of the cooling time and the gravitational free-fall time (t_cool/t_ff) falls below a critical value (∼ 10) the gas becomes susceptible to local thermal instability and fragments, leading to the formation of a multiphase medium consisting of cold dense clouds precipitating out of the hot diffuse ICM. The clouds then fall towards the central AGN, resulting in an increased accretion on the super massive black hole (SMBH) and feedback that, in turn, quenches runaway cooling in the cluster core. However, several recent works emphasize the importance of of explicitly including the gravitational potential of the central brightest cluster galaxy (BCG) to infer the acceleration due to gravity and the free-fall time in cool cluster cores. Recent observations which include the BCG gravity show that the observed threshold in min(t_cool /t_ff ) lies at a somewhat higher value, close to 20-30; there are only a few clusters in which this ratio falls below 10. In this talk, I will discuss numerical simulations of feedback Active Galactic Nucleus (AGN) jets interacting with the intracluster medium (ICM) with and without a BCG potential. We find that, for a fixed feedback efficiency, the presence of a BCG does not significantly affect the temperature but increases (decreases) the core density (entropy) on average. Most importantly, min(t_cool /t_ff ) is not affected much by the inclusion of the BCG gravity. I will speculate on the reasons behind the disagreement of observations and simulations. Further, the level of turbulence in the X-ray gas in the simulated cool-core clusters is consistent with Hitomi results on Perseus cluster.

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Gabriel Pratt

The Core-Excised Galaxy Cluster L-M Relation Evolves Self-Similarly

Presenter: Gabriel Pratt, CEA Saclay

Session: Samples and Scaling Relations II

Additional Authors: M. Arnaud, B.J. Maughan, J. Démoclès

         We show that the relation between the core-excised X-ray luminosity and the total mass (estimated from Yx) appears to evolve almost perfectly self-similarly, with surprisingly low scatter, at least up to z~0.9. Using synthetic samples, we perform quantitative tests to estimate the impact of selection effects and covariance on the result.

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Yu Qiu

The Interplay of Quasar & Radio-mode Feedback in Galaxy Clusters

Presenter: Yu Qiu, Georgia Institute of Technology

Session: Poster

Additional Authors: Tamara Bogdanović, Yuan Li, KwangHo Park, and John Wise
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         Recent observations find substantial amounts of cold gas in a number of cool-core clusters (CCCs). They also provide evidence that some CCCs host quasars in their brightest cluster galaxies (BCGs), raising questions about the importance of radiative feedback in such systems. Motivated by these findings we use 3D radiation-hydrodynamic simulations with the code Enzo to explore the joint role of the radio- and quasar-mode feedback from supermassive black holes (SMBHs) in BCGs. Our simulations show that the central SMBH transitions between the radiatively efficient and jet-dominated states on time scales corresponding to a few Gyr, where the duty cycle of each state depends on the amount of power allocated between the two feedback modes. Therefore, the observed fraction of CCCs that host quasars in their BCGs can be used to reveal the accretion and feedback cycles of these SMBHs.

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Thomas Reiprich

New Galaxy Groups & Clusters From the RASS

Presenter: Thomas Reiprich, Argelander Institute for Astronomy, Bonn University

Session: Samples and Scaling Relations II
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         Detailed XMM-Newton follow-up observations of large X-ray selected galaxy group and cluster samples are discussed. A new test to constrain the cosmological luminosity distance anisotropy using galaxy clusters is introduced and results indicating a violation of isotropy are shown. New X-ray selected very extended nearby galaxy groups and clusters have been discovered in ROSAT All-Sky Survey images at positions where no X-ray source was found previously; the properties of the cluster candidate sample (~1,000 in total) and implications for cosmological constraints from clusters are discussed. The expectations for Athena to discover and characterize early galaxy groups, massive and evolved enough to contain $>$10 million Kelvin gas, above redshift 2 are quantified.

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Juan Remolina Gonzalez

Einstein Radius Mass Estimates from Strong Gravitational Lensing

Presenter: Juan Remolina Gonzalez, University of Michigan

Session: Poster

Additional Authors: B. Reed, G. Mahler, K. Sharon
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         New surveys are discovering large numbers of galaxy clusters, including strong lensing clusters. Strong lensing offers a unique opportunity to study both the cluster itself and the background universe. While lens modeling provides measurements of the total projected mass distribution at the core of the cluster independent of assumptions on cluster astrophysics, this process is time consuming and computationally expensive. We would therefore like to use a faster method allowing us to process the large quantity of strong lensing clusters discovered. To first order, the projected enclosed mass can be determined from the observed Einstein Radius, by assuming spherical symmetry. This method has been extensively used in the literature, but its scatter has not yet been properly quantified. To address this, we use the Outer Rim N-body cosmological simulation. We find strong lensing clusters in an SPT-like cluster sample, and use ray tracing to produce lensed images of background sources. We compute the mass estimates from the Einstein Radius and compare them to the true mass of the clusters cores measured from surface density maps. Our analysis will provide for the first time an accurate assessment of the uncertainties in this method of mass estimates, and enable its use in large surveys.

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Angelo Ricarte

The Black Hole-Galaxy Connection in the RomulusC Simulation

Presenter: Angelo Ricarte, Yale University

Session: Poster

Additional Authors: Michael Tremmel, Priyamvada Natarajan
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         RomulusC is a simulation of a 10^14 solar mass cluster with specialized recipes for black hole dynamics and accretion. We reconstruct the assembly histories of hundreds of member galaxies and their supermassive black holes to determine what host galaxy properties drive black hole accretion. We find that the black hole accretion rate is directly proportional to the star formation rate--the so-called "AGN Main Sequence"--out to at least z=6. In addition, we find that the galaxy's incident ram pressure is responsible for halting black hole accretion after quenching the galaxy. Immediately prior to the final removal of gas, we often notice a boost in AGN activity, resulting in an increase in the AGN fraction with incident ram pressure. These results help inform semi-analytic models of supermassive black hole assembly.

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Gareth Roberg-Clark

Suppression of Electron Thermal Conduction in the High-Beta Intracluster Medium of Galaxy Clusters

Presenter: Gareth Roberg-Clark, University of Maryland

Session: ICM Microphysics: Observations and Theory

Additional Authors: J.F. Drake, C.S. Reynolds, M. Swisdak
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         Thermal conduction in weakly collisional, weakly magnetized plasmas such as the intracluster medium of galaxy clusters is not fully understood. One possibility is that plasma turbulence at the spatial and temporal scales of the electron larmor motion can scatter electrons and inhibit thermal fluxes. Here we present particle-in-cell (PIC) simulations and analytic analysis demonstrating this behavior. In our numerical model two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes electromagnetic whistler waves. The whistlers grow to large amplitude and resonantly scatter the electrons, strongly suppressing the heat flux. The rate of thermal conduction is controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. Unlike classical (Spitzer) thermal conduction, the resulting steady-state heat flux is largely independent of the thermal gradient and only weakly depends on the ambient temperature. The derived scaling law for thermal conduction has been confirmed in solar wind measurements. The impact of these results on thermodynamic stability of the ICM is being explored.

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Randall Rojas Bolivar

Attempting to Confirm the Presence of Inverse Compton Scattering in Abell 2163

Presenter: Randall Rojas Bolivar, University of Utah

Session: Poster

         Since the first non-thermal detections of Inverse Compton (IC) emission ingalaxy clusters at hard X-ray energies, we have yet to unambiguously confirm ICin follow-up observations. Claims of large IC fluxes from the 10' extent ofAbell 2163, a massive merging cluster at z=0.2, make it the next best chance ofconfirming a previous IC detection with NuSTAR. Additionally, recently availabledeep XMM data indicate extreme temperature variations (10-20 keV), the hottestof which are likely due to shocks. However, the XMM spectra suffer from variableGalactic absorption across the cluster, which can be avoided with NuSTAR'sharder energy band. We find that the global NuSTAR spectrum is consistent with pure thermal emission, although calibration issues remain. We also present a temperature map of the cluster and compare with previous maps made at lower energies.

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Mariachiara Rossetti

Properties of Planck-Selected vs X-ray Selected Galaxy Clusters: Evidence for Selection Biases

Presenter: Mariachiara Rossetti, IASF Milano - INAF

Session: Samples and Scaling Relations I

Additional Authors: F. Gastaldello, D. Eckert, M. Della Torre, G. Pantiri, M. Bertuletti, S. Molendi, S. Ghizzardi, S. De Grandi
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         The Sunyaev-Zeldovich effect provides an observational window to the intracluster medium, which is complementary to X-ray observations, and over the last few years has proved to be a mature technique to efficiently detect and characterize galaxy clusters. For instance, the Planck survey has mapped the whole microwave sky, detecting almost 2000 candidate massive clusters up to z~1, performing the first all-sky survey of galaxy clusters 20 years after the RASS. In my talk, I will review the properties of Planck-selected clusters, focusing on recent results about their dynamical and cool-core state and on their X-ray surface brightness profiles. I will show that the comparison of clusters properties in SZ-selected and X-ray selected samples can provide insights on selection effects, that I will discuss in the context of past and future X-ray surveys.

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Florian Ruppin

First High-Resolution SZ Mapping of a Galaxy Cluster with the NIKA2 Camera

Presenter: Florian Ruppin, University of Grenoble

Session: SZ
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         Our understanding of galaxy clusters up to high redshift will greatly benefit from high-angular resolution SZ observations. With both a wide field of view (6.5 arcmin) and a high angular resolution (17.7 and 11.2 arcsec at 150 and 260 GHz), NIKA2 is a KID-based camera that has been successfully installed and commissioned at the IRAM 30-m telescope (Pico Veleta, Spain). The NIKA2 guaranteed time program for the observation of galaxy clusters has started in 2017 and will allow us to characterize a large sample of clusters (~50) at redshifts above 0.5. These observations will serve multiple purposes such as the study of the redshift evolution of the scaling relation relating the SZ flux to the total mass of clusters. The observations of PSZ2 G144.83+25.11, the first cluster of the NIKA2 SZ large program, show very promising results. The potential of NIKA2 in terms of characterization of the ICM morphology and identification of high redshift sub-millimeter point sources is emphasized by the discovery of an over-pressure region in the south-west of the cluster and the SED extraction of a high redshift point source. The NIKA2 data are combined with the Mustang, Bolocam and Planck SZ observations of this cluster to constrain the electronic pressure distribution from the cluster core to its outskirts. XMM-Newton data is also combined with the NIKA2 SZ large program data within the framework of a joint X-ray and SZ imaging analysis that enable the characterization of the thermodynamical properties without relying on X-ray spectroscopy. I will present the characterization of the first NIKA2 SZ observations of a galaxy cluster at the IRAM 30-m telescope. I will then describe the ongoing SZ observation program with the NIKA2 camera and emphasize the synergy between the high quality NIKA2 SZ and XMM-Newton X-ray data for the calibration of the mass-obervable scaling relation.

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Mateusz Ruszkowski

Formation of Sharp Radio Edges in the AGN Feedback Simulations Including Sloshing

Presenter: Mateusz Ruszkowski, University of Michigan

Session: Nonthermal Phenomena I

Additional Authors: Karen Yang, John ZuHone, Maxim Markevitch
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         Spatial distribution of radio emission in cool core galaxy clusters (e.g., in the Virgo and Perseus clusters) often exhibits sharp frequency-independent edges. These features could be either due to AGN-inflated bubbles reaching the radius where the bubble entropy becomes comparable the entropy of the ambient intracluster medium, or due to sloshing motions associated with mergers and ordered magnetic fields that limit cross-field transport of cosmic rays responsible for the radio emission. In the absence of ordered fields, cosmic ray transport may tend to smear out any radio edges. We perform 3D MHD simulations of cool core galaxy clusters with radiative cooling, AGN feedback, substructure-induced sloshing motions, and cosmic rays physics. In particular, our simulations incorporate magnetic field aligned cosmic ray transport. We will present preliminary results from these simulations to assess whether radio plasma injected by the AGN could produce such sharp radio edges in the presence sloshing and significant magnetic-field aligned cosmic ray transport.

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Mohammadtaher Safarzadeh

The Fate of Gas-rich Satellites in Clusters

Presenter: Mohammadtaher Safarzadeh, Arizona State University

Session: Poster

Additional Authors: Evan Scannapieco

         We investigate the stellar mass-loss of gas-rich galaxies falling into clusters due to the change in the gravitational potential caused by the ram-pressure-stripping of their gas. We model the satellites with exponential stellar and gas disk profiles, assume rapid ram-pressure-stripping, and follow the stellar orbits in the shocked potential. Due to the change of the potential, the stars move from circular orbits to elliptical orbits with apocenters that are often outside the tidal radius, causing those stars to be stripped. We explore the impact of the redshift of infall, gas fraction, satellite halo mass, and cluster mass on this process. The puffing of the satellites makes them appear as ultra-diffuse galaxies, and the stripped stars contribute to the intracluster light. Our results show that these effects are most significant for less massive satellites, which have larger gas fractions when they are accreted into clusters. The preferential destruction of low-mass systems causes the red fraction of cluster galaxies to be smaller at lower masses, an observation that is otherwise difficult to explain.

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Jeremy Sanders

X-ray Measurements of Velocities in Clusters Using Gratings & CCDS

Presenter: Jeremy Sanders, Max Planck Institute for Extraterrestrial Physics (MPE)

Session: Velocities & Turbulence, Observations and Similations
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         There are few direct measurements of the velocity distribution of the intracluster medium in galaxy clusters. Unfortunately due to the loss of Hitomi, there is only a single calorimeter observation of the Perseus cluster. I will review our previous work using the RGS gratings on XMM-Newton to put constraints on the velocity width of the ICM in galaxy clusters, obtaining upper limits in some systems down to 300 km/s. I will also discuss our promising new work using the XMM EPIC-pn instrument to measure spatially-resolved bulk motions in galaxy clusters.

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Craig Sarazin

Merger Shocks in Clusters of Galaxies

Presenter: Craig Sarazin, University of Virginia

Session: ICM Microphysics: Observations and Theory

         X-ray and SZ observations of merger shocks in clusters of galaxies will be reviewed. The observations of shocks allow tests of the global dynamics and physical processes in cluster, including shock heating of electrons, Coulomb equipartition, thermal conduction, and nonthermal contributions to the shock energy. Comparisons to the radio continuum observations of radio relics leads to tests of models for particle acceleration and theories for the origin of radio relics.

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Jack Sayers

Imaging the Kinetic SZ Signal in a Sample of 10 Massive Clusters

Presenter: Jack Sayers, Caltech

Session: SZ

Additional Authors: Sunil Golwala, Tony Mroczkowski, Erik Reese, Grant Wilson, Mike Zemcov
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         I will present initial results from our kinetic SZ (kSZ) study of a sample of 10 massive galaxy clusters. Building upon our detection of the kSZ signal towards MACS J0717 using two-band Bolocam data, we have imaged 9 additional clusters to a similar depth. These images have sufficient resolution to detect large-scale inhomogeneities in the line of sight ICM velocity structure, allowing for a more complete understanding of potential merger scenarios when combined with X-ray imaging and spectroscopic velocity measurements. While some of the clusters in our study show no significant kSZ structure, others do show signs of a non-uniform line of sight velocity. For example, our images of Abell 697 show a gradient in the kSZ signal from ESE to WNW, indicating a velocity pattern that is in qualitative agreement with previous spectroscopic studies of cluster-member galaxies. In addition to describing these kSZ results, I will also present highlights from some of our recent multi-probe cluster studies involving SZ, X-ray, and/or lensing data. In particular, these studies have focused on constraining the amount non-thermal ICM pressure, ICM thermodynamic profiles near the virial radius, and cluster three-dimensional shapes.

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Keren Sharon

Strong Lensing Mass Reconstruction of the Frontier Fields Clusters

Presenter: Keren Sharon, University of Michigan

Session: Mass Profiles and Maps
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         I will describe the lensing community's effort to provide public mass and magnification models of the six Frontier Fields clusters; I'll present results, and discuss weaknesses and strengths of different algorithms.

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Timothy Shimwell

Galaxy Clusters in the LOFAR Two-Metre Sky Survey

Presenter: Timothy Shimwell, ASTRON

Session: Nonthermal Phenomena I

         The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120−168 MHz imaging survey that will eventually cover the entire Northern sky. Each of the 3170 pointings will be observed for 8 hrs, which, at most declinations, is sufficient to produce ∼5′′ resolution images with a sensitivity of ∼100 micro-Jy/beam and accomplish the main scientific aims of the survey which includes studying magnetic fields and particle acceleration mechanisms in clusters of galaxies. In this talk I will overview the present status of the survey with a specific focus on galaxy cluster science.

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Sinenhlanhla Sikhosana

Diffuse Radio Emission in ACTPol Clusters

Presenter: Sinenhlanhla Sikhosana, University of KwaZulu Natal, South Africa

Session: Poster
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         Non-thermal emission in clusters, in the form of diffuse radio emission, offers a different and vital perspective on intracluster medium processes. While radio halos and relics have been studied with increasing interest over the past decade there are still a number of open questions, such as the origin of the observed bimodality in the radio power vs. X-ray luminosity and the lack of diffuse emission in some merging clusters.We present uGMRT results for a subset of a large sample of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect, detected by the Atacama Cosmology Telescope project's polarimetric extension, ACTPol. This sample is uniformly selected and complete above a SZ mass of M500= 4x10^(14)M_sol, and for the first time includes clusters over a wider mass and redshift range than previous studies. The long baselines and dense core of the GMRT, coupled with the new UGMRT wide bandwith, make it an ideal instrument for diffuse radio emission detection in a project this size. Using newly developed inteferometric techniques for extracting extended, faint diffuse emission in the presence of bright, compact sources in wide-field continuum imaging data, we present early results of the UGMRT data, including new diffuse emission detection in two clusters.

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Miguel Socolovsky

The quenching of low-mass galaxies in distant galaxy clusters

Presenter: Miguel Socolovsky, University of Nottingham

Session: Poster

Additional Authors: Omar Almaini, Nina Hatch, Vivienne Wild

         I will present some recent results that provide insight into the quenching of low-mass galaxies in distant galaxy clusters between redshifts 0.5 and 1.0. We find candidate galaxy clusters by applying a friends-of-friends algorithm to the deep photometric data of the UKIDSS Ultra-Deep Survey. We use stellar mass functions and the stellar mass-size relation in order to conduct this study. The stellar mass functions reveal a strong excess of low-mass rapidly-quenched galaxies (i.e. post-starbursts) in cluster environments compared to the field. This indicates that low-mass objects are preferentially quenched in dense environments. The radial distributions of different galaxy populations as a function of cluster-centric distance show that galaxies quench on different timescales depending on their sSFR. Galaxies with high sSFR experience rapid quenching, with the star formation being truncated on timescales shorter than 1 Gyr, leading to a post-starburst phase. In contrast, galaxies with moderate sSFR are quenched more gradually. The study of the stellar mass-size relation reveals significant differences in the structure of high sSFR galaxies, the progenitors of cluster post-starburst galaxies. This provides clues to the mechanisms by which these galaxies were quenched by the cluster. In this talk I will review these findings and their discuss their implications for our current theories on the evolution of low-mass galaxies.

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Jubee Sohn

HectoMAP Galaxy Cluster Surveys

Presenter: Jubee Sohn, Harvard-Smithsonian Center for Astrophysics

Session: Poster
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         HectoMAP is a dense redshift survey covering a 53 deg2 of the sky enabling galaxy cluster surveys based on spectroscopy. We test the redMaPPer catalog and we use ROSAT All-Sky Survey (RASS) data to construct X-ray cluster catalog. We evaluate the redMaPPer membership probability spectroscopically and identify spectroscopic members of 104 redMaPPer cluster candidates. More than 90% of HectoMAP redMaPPer clusters have at least 10 spectroscopic members even at the low richness. Based on the HectoMAP and RASS data, we find 15 clusters (7 newly discovered) with redshift z ≤ 0.4 to the X-ray flux limit of the RASS (∼ 3 × 10^−13 erg s^−1 cm^−2). Three X-ray systems covered by Subaru/Hyper Suprime-Cam survey are impressive; one of them shows strong lensing arcs. The HectoMAP X-ray clusters have and Lx − σ scaling relation similar to that of known massive X-ray clusters. We predict that there are ∼ 12000 ± 3000 detectable X-ray clusters in the RASS, comparable to the estimate based on the XXL cluster survey (Pacaud et al. 2016).

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Taweewat Somboonpanyakul

The Clusters Hiding in Plain Sight (CHiPS) Survey

Presenter: Taweewat Somboonpanyakul, MIT

Session: Poster

Additional Authors: Michael McDonald
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         In this poster, I will introduce the beginning phase of the Cluster Hiding in Plain Sight (CHiPS) survey with the aim to discover new galaxy clusters surrounding X-ray-bright point sources. The CHiPS survey is designed around the idea that the centrally concentrated galaxy clusters or clusters hosting central QSOs can be misidentified as field active galactic nuclei (AGN) in previous all-sky surveys. As a pilot study, I will present our first newly discovered galaxy cluster, surrounding the quasar PKS1353-341, at z = 0.223, along with new Chandra observations of the galaxy cluster and its central AGN. By performing a detailed study of the object, we can investigate the impact a central quasar has on the intracluster medium and demonstrate the potential of the CHiPS survey to find massive nearby clusters with extreme central properties that may have been misidentified by previous surveys.

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M. W. Sommer, Kaustuv Basu

Results from a Systematic Search for Radio Halos in the Most Massive Clusters in the Universe

Presenter: Kaustuv Basu, University of Bonn (Lead author: M. W. Sommer)

Session: Poster

          We present recently published and in preparation results from our systematic search for giant radio halos in an SZ selected sample, comprising some of the most massive clusters in the universe. Radio data have been obtained with the Jansky-VLA interferometer at 1-2 GHz and the cluster sample is based on the Planck ESZ catalog. An early result (Sommer et al. 2017) is the discovery of Mpc-scale diffuse emission, consistent with giant radio halos, in two relatively relaxed systems hosting cool cores. These results lend tentative support to a "hybrid" model of giant radio halo emission in which some of the diffuse emission can be attributed to hadronic processes. In this high mass sample, we find a very high (~80%) fraction of clusters hosting radio halos. Similar high radio halo fraction in SZ selected samples were first reported in Sommer & Basu (2014) and also have been pointed out in more recent studies.

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Anatoly Spitkovsky

Electron Acceleration in Collisionless Shocks

Presenter: Anatoly Spitkovsky, Princeton University

Session: Nonthermal Phenomena I
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         I will review the recent advances in simulating shock structure and electron acceleration in collisionless shocks for a range of shock parameters. Electrons can be accelerated at both oblique and quasi-parallel shocks, and I will outline the efficiency of this process and the varying physical mechanisms responsible for acceleration in different regimes. The applications of these kinetic simulation results to cluster relics and accretion shocks will be highlighted.

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Sara Stanchfield

High Resolution SZ Imaging with Mustang-2 on the GBT

Presenter: Sara Stanchfield, University of Pennsylvania

Session: SZ

Additional Authors: Peter A. Ade, James Aguirre, Justus A. Brevik, Hsiao-Mei Cho, Rahul Datta, Mark J. Devlin, Simon R. Dicker, Bradley Dober, Shannon M. Duff, Dennis Egan, Pam Ford, Gene Hilton, Johannes Hubmayr, Kent D. Irwin, Kenda Knowles, Paul Marganian, Brian S. Mason,

         We present the array performance and early science results from MUSTANG-2, a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array operating on the Robert C. Byrd Green Bank Telescope (GBT). MUSTANG-2 is the first on-sky instrument to use microwave SQUID multiplexing and is available as a shared-risk/PI instrument on the GBT. In MUSTANG-2's first season, 7 separate proposals were awarded a total of 230 hours of telescope time. We present a summary of recent cluster observations from these proposals.

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Andra Stroe

Giant Cosmic Tsunamis: Reconciling Observations & Models of Cluster Radio Relics

Presenter: Andra Stroe, ESO

Session: Nonthermal Phenomena II
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         The merging of massive galaxy clusters can produce outward-travelling shock waves which shape the ICM at cluster outskirts. Giant radio relics trace these shock fronts and are thought to form when accelerated electrons emit synchrotron radiation in the presence of a constant magnetic field. I will present new very high-frequency radio observations which challenge the simple, widely accepted model for relic formation. Using unique observations spanning the 150 MHz to 30 GHz range, I will derive physical parameters, such as Mach numbers and electron ages, as well as constrain injection mechanisms. I will also discuss how new models involving re-acceleration of aged seed electrons or evolving magnetic fields can alleviate the discrepancies between observations of relics and theory.

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Kung-Yi Su

Stopping the Cooling Flow with Turbulent Stirring

Presenter: Kung-Yi Su, Caltech

Session: Cool Cores II: heating vs. cooling

Additional Authors: Philip F. Hopkins, Eliot Quataert, Christopher C. Hayward, Claude-Andre Faucher-Giguere, Dusan Keres, Xiangcheng Ma, Victor H. Robles
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         Cooling flow problem is important in galaxy clusters and >L* galaxies. We investigate the massive-galaxy end of the cooling flow problem using idealized, non-cosmological high-resolution hydrodynamic simulations with FIRE-2 (Feedback In Realistic Environment) stellar feedback model. The investigated galaxies have halo mass ranging from $10^{12}$ to $10^{14}$ solar mass. We find that various proposed solutions in the literature, including Type 1a supernovae, AGB winds, other stellar feedback, morphological quenching and magnetic fields, do not stop the cooling flow. Besides, our preliminary results show that although cosmic ray feedback can affect the star formation rate with sufficiently high energy density, it might not help much when the CR energy density is in equilibrium. On the other hand, a toy model where we include extra turbulent stirring does significantly reduce the cooling flow and quench the galaxy with an energy input rate ~10^42 erg/s . This provides hints on a potentially more realistic implementations of AGN feedback and constrains the kinetic energy input of the latter.

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Yuanyuan Su

Connecting the Micro & Macro Scale Astrophysics in Galaxy Clusters

Presenter: Yuanyuan Su, Harvard-Smithsonian Center for Astrophysics

Session: ICM Microphysics: Observations and Theory

Additional Authors: Ralph Kraft, Elke Roediger, Paul Nulsen, Alexander Sheardown , Thomas Fish, William Forman, Christine Jones, John ZuHone, Eugene Churazov

         The intracluster medium (ICM) approximates a highly ionized plasma. We present joint Chandra and XMM-Newton observations of the Fornax Cluster, the nearest southern cluster. In particular, we focus on its infalling galaxy NGC 1404, a low-entropy galaxy moving through the high-entropy ICM. The observations have revealed KHI eddies at its upstream cold front and mixed gas in its downstream stripped tail, indicating an inviscid and turbulent ICM. We have identified four sloshing cold fronts in the ICM spanning over two orders of magnitude in radius and falling onto the same spiral pattern. We speculate that all of these fronts were initiated by the infall of NGC 1404. We have also performed a full hydro + N-body simulation specifically tailored to Fornax and NGC 1404 to reproduce the merging scenario.

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Yuanyuan Su

HISAKI Observation of RCS2 J232727.6-020437: a Search for He I Lines in a massive cool core cluster at z=0.7s

Presenter: Yuanyuan Su, Harvard-Smithsonian Center for Astrophysics

Session: Poster

Additional Authors: Yuanyuan Su, Ralph Kraft, Tomoki Kimura, and the HISAKI science team

         Molecular cold gas and star formation have been observed at the center of cool-core clusters, although at a level much smaller than expected from the radiative cooling. Feedback from the supermassive black hole is likely to have prevented hot gas from cooling. However, the exact cooling and heating process remains unknown. The missing key piece is the link between the hot gas and cold gas. We present Hisaki observation of a massive cool-core cluster, RCS2 J232727.6-020437. We aim to detect gas of intermediate temperatures emitting He I$\alpha$ and He I$\beta$. At RCS2 J232727.6-020437's redshift, these Helium lines shift into the energy band of the extreme ultraviolet spectrometer onboard Hisaki and shift away from the absorption of the Galaxy. This study puts the first constraint on the amount of gas at $10^4-10^5$\,K at the center of a cool-core cluster. Our result suggests that the cooling process from hot gas to warm gas has been significantly suppressed at the cluster center.

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Paula Tarrío

A matched filter approach for blind joint detection of galaxy clusters in X-ray & SZ surveys

Presenter: Paula Tarrío, CEA

Session: Poster

Additional Authors: Jean-Baptiste Melin, Monique Arnaud
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         State-of-the-art galaxy cluster detection techniques rely on the analysis of single-survey observations, and in general, become less effective when trying to detect higher redshift clusters, of particular interest for cosmological analysis. Since the hot ionized gas of the intra-cluster medium emits thermal radiation in the X-ray band, and also distorts the cosmic microwave radiation via the Sunyaev-Zel'dovich (SZ) effect, combining these two complementary sources of information through innovative techniques can improve the cluster detection rate and reduce the number of false detections when compared to using only one of the probes. We present a novel cluster detection method that is able to combine observations from X-ray and SZ surveys by taking into account the specific characteristics of the observed signals and noise. This joint X-ray-SZ method is based on matched multi-frequency filters (MMF), and allows us to detect fainter or more distant clusters while maintaining high catalogue purity. The proposed method is tested using data from the ROSAT all-sky survey and from the Planck survey. With a first evaluation in the area of the sky covered by the SPT survey we show that thanks to the addition of the X-ray information, the joint detection method is able to achieve simultaneously better purity, better detection efficiency, and better position accuracy than its predecessor Planck MMF, which is based on SZ maps alone. For example, for a purity of 85%, the X-ray-SZ method detects 141 confirmed clusters in the SPT region; to detect the same number of confirmed clusters with Planck MMF, we would need to decrease its purity to 70%. The complete catalogue covering all the sky contains 2323 candidates, with a significant fraction that does not correspond to previously known clusters.

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Grant Tremblay

The Combined Power of ALMA & MUSE: Multiphase Velocity Structure of Cluster Galaxies

Presenter: Grant Tremblay, Harvard-Smithsonian Center for Astrophysics

Session: Cool Cores III: Rain and Fountains

         I will show stunning new ALMA and MUSE datacubes that map the cold molecular and warm ionized gas phases, respectively, for a diverse sample of cluster galaxies including cool core BCGs. These highly multidimensional datasets enable new, direct tests of major hypotheses stemming from, e.g., “Chaotic Cold Accretion”, “Precipitation”, and “Stimulated Feedback” models. To best illustrate the unified power of these new facilities, I’ll present several example galaxies in detail, and discuss new constraints from the enormous parameter space that can now be explored. I will leave the audience with a hands-on “tour” of what ALMA+MUSE joint analysis entails, using a Python-based Jupyter Notebook that all SnowCluster attendees can explore at their leisure.

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Michael Tremmel

The RomulusC Simulation: Exploring Galaxy Evolution in Clusters at High Resolution

Presenter: Michael Tremmel, Yale University

Session: Galaxies in and Behind Clusters

Additional Authors: Tom Quinn, Arif Babul, Angelo Ricarte, Priyamvada Natarajan, Urmila Chadayammuri, Andrew Pontzen, Marta Volonteri, Daisuke Nagai
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         We present RomulusC, the highest resolution simulation to date of a 10^14 Msun halo run with full hydrodynamic treatment to z = 0 and including models for star formation and supermassive black hole (SMBH) physics. We show how the sub-grid models for stellar physics and SMBH growth and feedback presented in Tremmel et al. (2017), which have been constrained to reproduce observations only at much lower masses (10^12 Msun halos and below), result in a galaxy cluster with realistic internal structure as well as a quenched brightest cluster galaxy with a z= 0 stellar mass consistent with observations. We show how large scale outflows driven by the active central SMBH are able to quench star formation while maintaining a cool core structure. Because of our unprecedented spatial (250 pc) and mass (2x10^5 Msun) resolution, we are also able to track the evolution of satellite galaxies down to stellar masses of 10^8 Msun, finding a dearth of both star formation and black hole activity relative to the field population in Romulus25. We predict that the majority of satellites down to stellar masses of 10^8 Msun will be quenched by z = 0 and that this quenching, as well as the lack of SMBH activity, is the result of ram pressure stripping.

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Nhut Truong

Mass-ICM Metallicity Relation From Simulations & Observations of Galaxy Clusters

Presenter: Nhut Truong, Hot Universe Research Group, MTA-Eötvös University Lendület

Session: Abundances

Additional Authors: Francois Mernier, Norbert Werner, Elena Rasia, Veronica Biffi, Susana Planelles, Massimo Gaspari, Stefano Borgani
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         Recent X-ray observations of galaxy clusters show that the distribution of metallicity in the intra-cluster medium (ICM) is remarkably uniform in space and time. By applying a consistent analysis in simulated and observed samples we study how this quantity depends on cluster total mass and on the ICM temperature. We find only a mild variation of the metal abundance from groups to clusters. We looked at potential biases that might affect observational analyses such as the dependence on cluster core properties. No significant deviation is found between cool-core and non-cool core systems regarding to the mass (or temperature) dependence of the ICM metallicity. Finally, we predict the evolution of the mass-metallicity relation up to the redshifts that will be reached by future X-ray missions, e.g. ATHENA.

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Evan Tucker

Simultaneously Modeling the Internal Dynamics & Substructure of Abell 267

Presenter: Evan Tucker, Carnegie Mellon Univeristy

Session: Poster

Additional Authors: Matthew G. Walker
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         I will present a dynamical analysis of Abell 267 (z~0.23) using new spectra observed with Magellan/M2FS. Our sample includes ~220 individual galaxy spectra along the line-of-sight to Abell 267. For each galaxy, we measure redshift as well as mean age, metallicity, alpha enrichment, and internal velocity dispersion of the stellar population. We applied a new method to simultaneously obtain Bayesian estimates for the internal kinematics and substructure of the cluster. For the main cluster population, we implement a cluster rotation model in combination with a Jeans analysis, which is embedded within a mixture model that explicitly accounts for member and contamination galaxies as well as any subpopulations. We find that with this comprehensive model, we are able to disentangle effects of subpopulations and cluster rotation, revealing a relatively clear view of Abell 267's dynamical status and gravitational potential.

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Shutaro Ueda

Coexistence of Excess Hot Gas & a Sloshing Cool Core in RXJ1347.5-1145

Presenter: Shutaro Ueda, ISAS/JAXA

Session: SZ

Additional Authors: Tetsu Kitayama, Masamune Oguri, Takuya Akahori, Daisuke Iono, Takumi Izumi, Ryohei Kawabe, Eiichiro Komatsu, Kotaro Kohno, Hiroshi Matsuo, Naomi Ota, Yasushi Suto, Shigehisa Takakuwa, Motokazu Takizawa, Takahiro Tsutsumi, and Kohji Yoshikawa
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         We present the results of multi-wavelength study of a merging cluster RXJ 1347.5-1145 using Chandra, Atacama Large Millimeter/submillimeter Array (ALMA), and HST. We identified the peak position of excess hot (~ 30 keV) intracluster medium (ICM) in the southeast substructure, whose region is faint at X-rays but the signal of the Sunyaev-Zel'dovich effect (SZE) is prominent. The HST strong-lensing analysis shows the presence of a secondary component of dark matter halo. Its mass peak agrees well with the position of an infalling subcluster, while we found a clear offset between its mass peak and the substructure in X-rays and the SZE. These results indicate that the ICM originally in the subcluster is recently stripped and heated by merger shock. We also found a spiral pattern in the core after subtracting the mean X-ray surface brightness. This means that gas sloshing occurs in the cool core. RXJ 1347.5-1145 is therefore the first cluster ever known to host both the shock-heated excess hot ICM and the sloshing cool core. We will discuss more details of the merger in this cluster.

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Keiichi Umetsu

CLASH Lensing View of the Formation & Evolution of Galaxy Clusters

Presenter: Keiichi Umetsu, ASIAA, Taiwan

Session: Samples and Scaling Relations I
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         I will talk about the recent discovery (Fujita, Umetsu, Rasia, Meneghetti, Donahue, Medezinski, Okabe, & Postman ) of a universal "plane" dictating dark-matter halo evolution from our gravitational lensing and X-ray observations from the CLASH survey. We show that high-mass galaxy clusters lie on a plane in the three-dimensional logarithmic space of their characteristic halo radius "rs", mass "Ms" , and X-ray temperature "Tx" with a very small orthogonal scatter. The tight correlation indicates that the gas temperature was determined at a specific cluster formation time, which is encoded in (rs,Ms) and that the gas was heated when the clusters were in the fast-growing phase. Intriguingly, the plane is significantly tilted with respect to the canonical virial expectation, Tx ∝ Ms /rs. We show that the self-similar solution of Bertschinger (1985) for secondary infall and accretion can explain the observed relation, Tx ∝ Ms^1.5 /rs^2. Numerical simulations reproduce the observed plane and its angle. This result holds independently of the gas physics implemented in the code, revealing the fundamental origin of this plane.

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Igone Urdampilleta

X-ray study of the double radio relic Abell 3376

Presenter: Igone Urdampilleta, SRON/Leiden Observatory

Session: Poster

Additional Authors: Hiroki Akamatsu, Francois Mernier, Jelle S. Kaastra, Jelle de Plaa, Takaya Ohashi, Yoshitaka Ishisaki, Hajime Kawahara
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         We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 (z = 0.046), observed with the Suzaku XIS instrument. These deep (~360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a strong shock (Mw = 2.8 ± 0.4) in the western direction at r~26 arcmin, derived from a temperature and surface brightness discontinuity across the radio relic. In the East, we detect a cold front at r~3 arcmin and a weaker shock (Me = 1.5 ± 0.1) at r~8 arcmin, possibly associated to the 'notch' of eastern relic. Based on the shock speed derived from the Mach numbers, we estimate that the dynamical age of the shock front is ~0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and the merger is taking place close to the plane of the sky. These results are consistent with simulations, optical and weak lensing studies from the literature.

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Sravani Vaddi

Ghost Ionization In Cooling Flow Filaments Of Galaxy Clustersghost Ionization In The Cooling Flow Filaments Of Galaxy Clusters

Presenter: Sravani Vaddi, National Center for Radio Astrophysics (NCRA-TIFR)

Session: Poster

Additional Authors: Grant Tremblay, Chris O'Dea, Susmita Chakravorty, Stefi Baum,

         Heating by AGN through outflows has gained fundamental importance in the study of large-scale structure and galaxy formation and is often invoked to quench the radiative cooling of the hot intracluster medium (ICM) onto the brightest cluster galaxy (BCG). However, in cool-core clusters where the ICM cooling rate is shorter than the age of the cluster, AGN heating does not completely offset radiative losses and significant additional ionization mechanism is necessary to explain the observed temperature and line ratios of the filamentary emission line nebulae around the cool core BCGs. In an effort to find the source of this mysterious ionization, we have obtained deep FUV spectroscopy using the HST cosmic origins spectrograph of the filaments of two cool-core galaxy clusters A2597 and ZW3146. Unlike in the optical, spectral diagnostics in the FUV are more capable of discriminating between various heating/ionization models (for e.g., stellar photoionization, thermal conduction, cosmic ray heating, and shock heating). Using photoionization codes MAPPINGS and CLOUDY, various ionizing sources have been simulated and these simulations consist of single and hybrid models. In general, we notice that there is no one single model that provides a satisfactory explanation for the ionization state of gas. However, we show that stellar and AGN photoionization alone are not enough to ionize the nebula in A2597 and speculate that, shock heating is the likely ionizing source.

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Frank van den Bosch

The Tidal Evolution of Substructure

Presenter: Frank van den Bosch, Yale University

Session: Advances in Simulations

Additional Authors: Go Ogiya
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         Hierarchical structure formation in a LCDM cosmology gives rise to virialized dark matter halos that contain a wealth of subtructure. Being able to accurately predict the abundance and demographics of dark matter subhaloes is of paramount importance for many aspects of cluster physics. Dark matter substructure is subject to tidal stripping and tidal heating, which are highly non-linear processes and therefore best studied using numerical N-body simulations. Unfortunately, as I will demonstrate, state-of-the-art cosmological simulations are unable to adequately resolve the dynamical evolution of dark matter substructure. They suffer from a dramatic amount of artificial subhalo disruption as a consequence of both inadequate force softening and a discreteness-driven runaway instability that is amplified in the presence of a tidal field. I discuss implications for a variety of topics related to galaxy clusters, and briefly discuss potential ways forward.

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Alexander van Engelen

Ionized Gas in Galaxy Clusters Using the CMB

Presenter: Alexander van Engelen, Canadian Institute for Theoretical Astrophysics

Session: SZ

Additional Authors: Nicholas Battaglia, Vera Gluscevic, Joel Meyers, P. Daniel Meerburg, Kendrick Smith
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         Upcoming CMB observations will reveal a wealth of astrophysics from galaxy clusters. I will discuss two new observational effects to which future surveys will be sensitive, in addition to the well-known thermal and kinetic Sunyaev-Zel’dovich effects. The first is the polarized Sunyaev-Zel’dovich effect, which arises from scattering from the incident CMB quadrupole. The second is differential screening of the background CMB due to Thomson scattering in the clusters. Both of these effects can be used to measure the free electron density profile in a manner that is independent of the thermal state of the gas, and can be used to normalize relationships between the total electron gas mass and other observables such as thermal SZ and X-ray brightness. Additionally, I will show how observations of the polarized Sunyaev-Zel’dovich effect at low redshift can be used to indirectly constrain the reionization history at high redshift.

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Reinout van Weeren

Low-Frequency Radio Observations of ICM Cosmic Rays

Presenter: Reinout van Weeren, Leiden University

Session: Nonthermal Phenomena I

         Diffuse extended radio sources in galaxy clusters reveal the presence of cosmic rays and magnetic fields in the ICM. The bulk of the radio emission from these cosmic rays is emitted at low radio frequencies. In this talk I will give an overview of recent radio studies of clusters, mostly carried out with LOFAR.

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Adrian Vantyghem

Molecular Gas Flows in Central Cluster Galaxies

Presenter: Adrian Vantyghem, University of Waterloo

Session: Cool Cores III: Rain and Fountains

Additional Authors: Brian McNamara, Helen Russell, Alastair Edge
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         Molecular gas is thought to connect the cooling of the intracluster medium to accretion onto nuclear supermassive black holes, fueling the powerful radio jets that pump energy back into the surrounding medium. ALMA observations are revealing 5-20 kpc long molecular filaments, with almost no signs of long-lived, rotationally-supported nuclear structures. These filaments frequently trail X-ray cavities, suggesting that molecular clouds are formed in situ from intracluster gas uplifted by X-ray cavities. I will present recent ALMA results from two other systems, RXCJ1504.1-0248 and RXJ0821.0+0752, where the uplift model breaks down. In RXJ0821, all 10^10 solar masses of molecular gas is offset from the galactic center, and is too heavy to have been lifted by the X-ray cavity. RXCJ1504 hosts a 20 kpc long filament that is not clearly coupled to an X-ray cavity.

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Rukmani Vijayaraghavan

The Destruction of Galaxies in Extreme Environments

Presenter: Rukmani Vijayaraghavan, University of Virginia

Session: Galaxies in and Behind Clusters

Additional Authors: Craig Sarazin, Paul Ricker

         Clusters of galaxies are hostile environments: galaxies are subject to strong tidal forces and ram pressure that remove dark matter, stars, and gas; heat conduction can rapidly evaporate gas unless suppressed by magnetic fields; galaxies interact and collide in these dense regions. Galaxies themselves can amplify cluster magnetic fields and inject turbulence in the ICM. Mergers between clusters can accelerate these processes -- for instance, merger shocks can rapidly strip gas, and brief periods of increased galaxy density can lead to increased galaxy interactions. The net impact of these phenomena are to stop star formation resulting in 'red and dead' passive galaxies. Using the results of numerical simulations, I will describe these phenomena and their observational implications -- the destruction of galaxies, their short-lived influence on the cluster environment, the brief periods of merger activity that have long-term consequences, and detecting the remnants of these mergers.

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Mark Voit

Feedback & the Precipitation Limit

Presenter: Mark Voit, Michigan State University

Session: Cool Cores III: Rain and Fountains
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         The central supermassive black hole in a galaxy cluster appears to provide the energetic feedback that regulates central star formation. Understanding how that feedback loop becomes finely tuned has been challenging, but accumulating evidence is increasingly indicating that the feedback loop is closed by condensation of cold gas clouds that precipitate out of the circumgalactic medium and rain down onto the central black hole. I will outline the evidence favoring this mechanism and will comment on recent theoretical advances in understanding of how it works.

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Stephen Walker

Unravelling the Physics of the ICM with Cold Fronts

Presenter: Stephen Walker, NASA Goddard Space Flight Center

Session: ICM Microphysics: Observations and Theory
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         Deep observations of nearby galaxy clusters with Chandra have revealed mysterious concave ‘bay’ structures in the central regions of a number of systems (Perseus, Centaurus and Abell 1795), which have similar X-ray and radio properties. These bays have all the properties of cold fronts, where the temperature rises and density falls sharply, but are concave rather than convex. By comparing to simulations of gas sloshing, we find that the bay in the Perseus cluster bears a striking resemblance in its size, location and thermal structure, to a giant (50 kpc) roll resulting from Kelvin-Helmholtz instabilities. Moving away from cluster cores, I will present new deep Chandra observations of the outer regions of the Perseus cluster, providing the clearest view of a colossal large scale cold front lying at half the cluster virial radius. We have found exciting new structures in this cold front, providing powerful new insights into the physical properties of the ICM.

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Norbert Werner

Heating vs. Cooling in the X-Ray Emitting Atmospheres of Giant Elliptical Galaxies

Presenter: Norbert Werner, MTA-Eotvos/Masaryk/Hiroshima University

Session: Cool Cores I: Statistics, Formation and Destruction

         I will present a detailed study of heating and cooling in the hot X-ray emitting atmospheres for a variety of nearby early-type galaxies, such as massive relic galaxies (zero redshift red nuggets), fast rotating S0 galaxies, and for systems with unusually strong jets. Finally, I will discuss the results of a systematic Chandra X-ray study of the connection between the properties of the hot haloes and the cooler Hα+[NII] emitting phase in a sample of 49 nearby X-ray and optically bright early type galaxies.

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Joshua Wiener

High Beta Effects on Cosmic Ray Streaming in Galaxy Clusters

Presenter: Joshua Wiener, UW Madison

Session: Nonthermal Phenomena II

Additional Authors: Ellen Zweibel, S. Peng Oh
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         Diffuse, extended radio emission in galaxy clusters, commonly referred to as radio halos, indicate the presence of high energy cosmic ray (CR) electrons and cluster-wide magnetic fields. We can predict from theory the expected surface brightness of a radio halo, given magnetic field and CR density profiles. Previous studies have shown that the nature of CR transport can radically effect the expected radio halo emission from clusters. Wiener, Oh, and Guo 2013 showed that reasonable levels of magnetohydrodynamic (MHD) wave damping can lead to super-Alfvenic CR streaming speeds. But a careful treatment of MHD waves in a high beta plasma, as expected in cluster environments, reveals damping rates may be enhanced by a factor of beta^1/2. This leads to faster CR streaming and lower surface brightnesses than without this effect. In this work we re-examine the simplified, 1D Coma cluster simulations (with radial magnetic fields) of Wiener, Oh, and Guo 2013 and discuss observable consequences of this high beta damping. Future work is required to study this effect in more realistic simulations.

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Daniel Wik

Electron Heating & Acceleration at Galaxy Cluster Shocks: Insights From NuSTAR

Presenter: Daniel Wik, University of Utah

Session: ICM Microphysics: Observations and Theory
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         Mergers between galaxy clusters drive weak shock fronts into the intracluster medium, capable of both heating the gas and accelerating relativistic particles. Measurements of the high temperature gas and non-thermal inverse Compton (IC) emission that result from these shocks most benefit from sensitive observations at hard X-ray energies. Recent observations of the massive merging clusters Abell 2163, Abell 665, and the Bullet cluster with NuSTAR, the first focusing hard (>10 keV) X-ray observatory, improve measurements of both thermal and IC components in each cluster. In the Bullet Cluster, we jointly fit long Chandra and NuSTAR observations--totaling 1 Ms--to constrain the temperature of the bow shock and determine whether electrons are directly heated by the shock front as previously suggested by Chandra data alone. We also preview NuSTAR constraints on the temperature of the recently discovered shock in Abell 665 and on the flux of IC emission from the electrons producing radio halos in all three clusters.

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Jon Willis

HST/WFC3 Spectroscopic Confirmation of XLSSC122: a Mature X-ray/SZ Detected Cluster at z=2?

Presenter: Jon Willis, University of Victoria

Session: Distant clusters

Additional Authors: R.E.A. Canning, A. King, S.W. Allen, R.G. Morris, S.A., Stanford, E. Noordeh, A. Mantz
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         We present cycle 25 HST/WFC3 grism spectroscopy of the cluster XLSSC 122 that confirms a redshift of z=1.98. XLSSC 122 was identified as an extended X-ray source in the XMM-LSS/XXL survey and was subsequently detected as SZ decrement toward the CMB. A 100 ks XMM exposure further characterised the cluster as displaying T=5 keV, Z=0.33 Zsolar and M500=6.3e13 Msolar. In a striking result, the redshift z=1.99 derived solely from spectral fitting of the redshifted Fe 6.7keV feature is in precise agreement with the redshift obtained from HST IR spectroscopy. XLSSC122 displays a clear red sequence and overall presents a red fraction of 0.6 for member galaxies with Ks<23AB. In this talk we present our cycle 25 HST observations, redshift determination and analysis of the F105W-F140W cluster colour magnitude diagram. We discuss whether, given a metal-rich, hot ICM hosting a relatively populous red sequence, XLSSC 122 represents a mature, yet low-mass cluster at a look-back time of 10 Gyr.

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Grant Wilson

Millimeter Imaging of Clusters with TolTEC/LMT

Presenter: Grant Wilson, University of Massachusetts

Session: Future Instruments

Additional Authors: on behalf of the TolTEC Collaboration
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         TolTEC is a new camera being built for the 50-meter Large Millimeter-wave Telescope (LMT) in Puebla, Mexico to survey clusters, distant galaxies and star-forming regions in the Milky Way. The optical design simultaneously couples the sky onto focal planes at 150, 220, and 280 GHz and provides diffraction limited imaging over the 4 arcminute field of view of the telescope with FWHM resolution of 10”, 6.5”, and 5” respectively. The combination of moderate resolution, raw detector count, and the large dish give TolTEC unprecedented sensitivity to imaging astrophysical processes inside clusters as traced by both the thermal and kinetic SZE. In this talk I will review the instrument’s projected sensitivities as well as our plans to conduct large-scale public surveys across all domains of millimeter astronomy.

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Michael Wise

When Physics Collide: AGN Feedback in the Merging Cluster Cygnus A

Presenter: Michael Wise, ASTRON Netherlands Institute for Radio Astronomy

Session: Cool Cores II: heating vs. cooling

Additional Authors: M. N. de Vries, P. E. J. Nulsen, B. T. Snios, T. L. R. Halbesma, J. M. F. Donnert, M. Birkinsaw, D. M. Worrall, R. T. Duffy, J. P. McKean, D. A. Rafferty, B. R. McNamara, A. C. Edge, M. J. Hardcastle, J. H. Croston, W. G. Mathews, R. A. Perley, C. L. Cari

         AGN feedback and ongoing mergers are arguably the two dominant physical processes driving the formation and evolution of clusters over cosmic time. Taken together, these mechanisms determine the energetic history of the ICM in clusters and manifest a range of thermal and non-thermal emission that have been extensively studied using X-ray, radio, and other observations. Although both of these mechanisms are fairly ubiquitous in cluster systems, most studies have tended to focus on one mechanism or the other in specific systems. The direct interplay between these two processes has largely been inferred but not observed. The merging cluster system containing the well-known Cygnus A radio galaxy, however, represents a rare opportunity to observe both of these ongoing physical processes in a single system and, more importantly, the direct interaction between them. In this presentation, we will show results from a new, deep 2.2 Msec observation of the Cygnus A cluster system obtained as part of the Chandra XVP program. A detailed spatial and spectral analysis of the large-scale X-ray emission in the system reveal an ongoing, equal mass major merger and, when combined with numerical modelling, provide constraints on the merger geometry. We also find strong evidence for long-term, episodic output from the central AGN in Cygnus A over the past 400-500 Myr. In addition to the energy deposited into the ICM by the shock from the ongoing major merger, we derive the frequency, duration, and energetic output of the AGN in Cygnus A over this same timescale.

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Denis Wittor

On the Depolarization of the Observed Emission From Radio Relics

Presenter: Denis Wittor, University of Bologna

Session: Nonthermal Phenomena II

Additional Authors: Matthias Hoeft, Franco Vazza, Marcus Brüggen
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         Highly polarized, large-scale synchrotron emission is found in the outskirts of galaxy cluster in form of Radio Relics, which trace shock waves produced during cluster mergers. The study of Radio Relics provides information both on the shock acceleration of cosmic-ray electrons at large scales and on the topology of the underlying large-scale magnetic fields. In this talk, I will discuss how the the combination of state-of-the-art cosmological MHD simulations with ENZO with my new Lagrangian tracer code CRaTer allows us to study the properties of the polarized emission of Radio Relics in detail. This novel approach allows us to isolate the different regions of depolarization and estimate their impact on the observed polarized emission of Radio Relics, which is crucial to interpret existing and future observations of polarised emission observed at radio wavelengths.

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Ka-Wah Wong

Scaling Relations at R200 & Implications for Physics in Cluster Outskirts

Presenter: Ka-Wah Wong, Minnesota State University, Mankato & Eureka Scientific

Session: Samples and Scaling Relations II
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         With the growing number of galaxy clusters and groups measured in X-ray out to R200, it is possible to study the scaling relations for the enclosed gas fraction (fgas,200) and entropy (K200) versus temperature (T500), where the gas fraction and entropy are of great interest to constrain cosmological parameters and to understand the thermodynamic history of clusters or group formations, respectively. We will present scaling relations using more than 20 groups and clusters with published X-ray data in the literature. The power law slope of the K200-T200 relation is significantly shallower than the gravity heating-only baseline model, in contrast to that at R500. For massive clusters (T500 > 2 to 3 keV), K200 is lower than the baseline model, while no such entropy deficit was found for low-mass groups. The entropy deficit at R200 for massive clusters cannot be fully accounted for by the bias or deviation in the gas fraction. The enclosed baryon fraction at R200 is broadly consistent with the cosmic value. We will discuss the diversity of low mass groups out to R200 and their difference from massive clusters, as well as implications for physics in cluster outskirts.

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Hiroya Yamaguchi

Metal Abundances of the Perseus Cluster with Hitomi High-Resolution Spectroscopy

Presenter: Hiroya Yamaguchi, NASA/GSFC, Univ of Maryland

Session: Hitomi Results
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         The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae. Therefore, X-ray spectroscopy of the intracluster medium (ICM) provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the Fe-peak elements (i.e., Cr, Mn, Fe, Ni) is key to understanding how the progenitors of typical Type Ia supernovae evolve and explode. Because the K-shell transition lines of Cr and Mn are weak, and those of Fe and Ni are so close in energy, high resolution X-ray spectroscopy is required for a precise determination of their abundances. I present observations of the Perseus Cluster performed with the Soft X-ray Spectrometer (SXS) on board the Hitomi X-ray Observatory to obtain significant detections of the weak resonance lines of Cr, Mn, and Ni. Our measurements reveal that these elements have near-solar abundance ratios with respect to Fe, in contrast to previous X-ray measurements of ICM abundances. The observed abundance pattern can naturally be explained by taking into account a combination of near- and sub-Chandrasekhar-mass Type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment.

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Jun Yang

Is M33 X-8 A Pulsar? X-Ray Properties As Observed By Nustar

Presenter: Jun Yang, University of Utah

Session: Poster
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         The bright ultraluminous X-ray source (ULX), M33 X-8, has been observed couple times by NuStar (Nuclear Spectroscopic Telescope Array), providing us an unique opportunity to search for pulsations with the simultaneous detections from two instruments. From NuSTAR observation with ID of 50310002001, instrument A detected its 769.42 $\pm$ 4.87 s spin period, and instrument B detected the pulsations with 724.82 $\pm$ 5.22 s. Therefore, M33 X-8 is a pulsar candidate with a spin period of 725s. Its predicted orbital period is around 198 days.

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Jorge Zavala

Galaxies' Gas Supply In High-Redshift Protoclusters

Presenter: Jorge Zavala, UT Austin

Session: Poster

Additional Authors: Caitlin Casey, et al.

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         Taking census of the protocluster's gas supply -and to compare it to a sample of mass-matched galaxies in normal environments- is crucial to understand how environment impact the growth of galaxies. Here, we will present ALMA continuum observations of LBGs in two protoclusters at z~2.5. Using this data, we derive gas masses and star-formation efficiencies and compare them with a control sample in the field. These results, and their implications for the star formation activity of galaxies in overdense environments , will be discussed.

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Stephan Zimmer

Gamma-ray Constraints on Intracluster Cosmic Rays

Presenter: Stephan Zimmer, University of Innsbruck

Session: Nonthermal Phenomena II
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         I will review the current status of gamma-ray observations of clusters of galaxies and how these observations can be turned into constraints on the physics of cosmic rays in the intracluster medium.

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Elad Zinger

Illustris TNG: AGN Feedback in Massive Halos

Presenter: Elad Zinger, Max-Planck-Institute fur Astronomie

Session: Poster
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         The Illustris TNG (The Next Generation) is a suite of Cosmological, Magneto-Hydrodynamical Simulations, run with the AREPO code on boxes of size 50, 100 and 300 Mpc on a side, thus affording high resolution treatment alongside a large statistical sample of objects. We present the simulation suite with a focus on group- and cluster-sized objects, and show the effects of the AGN Feedback in setting the conditions in the galaxies and ICM of massive halos.

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John ZuHone

Probing the Plasma Physics & Kinematics of the Intracluster Medium with X-Ray Observations & Simulations

Presenter: John ZuHone, Harvard-Smithsonian Center for Astrophysics

Session: Velocities & Turbulence, Observations and Similations

         Since its launch in 1999, the Chandra X-ray Observatory has providedunprecedented views of the hot plasma of galaxy clusters, revealingstructures such as shocks, cold fronts, and indications of gasturbulence. Before its unfortunate demise, the Hitomi mission provided thefirst direct measurements of gas motions in the Perseus cluster. All ofthese observations indicate the intracluster medium (ICM) has interestingplasma properties and is continuously stirred by gas motions large andsmall driven by mergers and AGN feedback. In this talk, I will presentthe results of a number of hydrodynamical simulations of galaxy clustermergers and compare them to observations with a view towards constrainingthe plasma and kinematic properties of the ICM. I will finish my talkwith a view toward future X-ray missions and what may be revealed in thecluster plasma by the combination of high spectral and spatial resolution.

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The 4th SnowCluster workshop is graciously supported by:
 
 

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