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Abstracts By Presenter's Last Name


Toma Badescu (Poster)

Discovery of a Proto-cluster Associated with a Lyman Alpha Blob Pair at z=2.3

Presenter: Toma Badescu, Argelander-Institut für Astronomie, Bonn, Germany
Additional Authors: Yujin Yang, Frank Bertoldi, Ann Zabludoff, Alexander Karim, Benjamin Magnelli


         Galaxy cluster progenitors, also known as protoclusters, are matter and dark-matter structures at high redshifts, which will collapse into virialized clusters by z = 0. These progenitors can be found through narrowband surveys detecting overdense regions of galaxies at a given redshift. Previous studies suggest that bright Lyα blobs — extended nebulae with sizes of ~100kpc and Lyα luminosities of ~1044 erg/s — preferentially reside in over-dense regions, thus could be used as markers of protoclusters. To investigate this hypothesis and look for new protoclusters, we present deep, wide-field Lyα narrowband imaging of a 1° x 0.5° region around a known Lyα blob pair at z = 2.3, which was originally discovered by a blind survey. We find 183 Lyα emitters, including the Lyα blob pair and 3 new intermediate Lyα blobs. Using these Lyα emitters as tracers, we discover a new proto-cluster (Bootes J1430+3522) associated with the Lyα blob pair, with a surface density contrast of 2.7, a de-projected volume density contrast of δ ~ 10, and a projected diameter of ~20 comoving Mpc. By comparing with cosmological simulations, we conclude that this large-scale structure is likely to evolve into a present-day Coma-like cluster with log(M/M) ~ 15.1+-0.2. Our discovery of a proto-cluster around the Lyα blobs show that Lyα blobs are markers for overdense regions or protoclusters. However, combined with previous wide-field Lyα emitter surveys, we find that Lyα blobs tend to reside in the outskirt of protoclusters and over-represent the moderately overdense region (δS = 1-2). We speculate that Lyα blobs may represent proto-groups that are accreting into more massive proto-clusters, and that the Lyα-emitting gas is a precursor of the intra-group medium.

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Joanna Bridge

Characterizing Lyman-Alpha Scattering in Nearby Galaxies

Presenter: Joanna Bridge, Pennsylvania State University
Additional Authors: Matthew Hayes, Jens Melinder, Göran Östlin, Caryl Gronwall, Robin Ciardullo


         The hydrogen emission line of Lyman alpha (Lyα) has long been recognized as key to studying high redshift star-forming galaxies. However, due to the resonance of the emission line, the path that a Lyα photon takes from emission to eventual escape from the galaxy is essentially a mystery. This scattering poses a problem for using Lyα as a key emission feature of galaxies because it results in Lyα not being observed in all star-forming galaxies, and, in galaxies where it is observed, the place where the photon is originally emitted and where it is observed are two very different things. We discuss here how the Lyman-Alpha Reference Sample (LARS) provides a unique sample of 14 nearby (0.02 < z < 0.2) galaxies in which we investigate the role of scattering, both on the global scale of the galaxies and down to scales of ~ 50 parsecs using Hubble Space Telescope imaging. We compare the Lyα/Hα ratios with those expected from pure dust attenuation models, finding that in some cases significant positive departures are found on small scales, consistent with geometric effects being important on sizes comparable to the HII regions. We then develop a simple scattering model in which we are able to estimate the average path length a Lyα photon travels with respect to non-resonant radiation, and quantify the excess dust optical depth to which Lyα radiation may be susceptible.

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Zheng Cai

Giant Lyman-Alpha Nebulae in the Extremely Massive Overdensities

Presenter: Zheng Cai, UCO/Lick Observatory

         The current galaxy formation theories suggest that a significant amount of gas accretes onto galaxies from the IGM in a cold T ~ 104 K phase, and such cool gas should be detectable in diffuse Ly-alpha emission. Recently, our deep KPNO-4m, Bok narrow-band imaging, and Palomar/CWI IFU observations have revealed a sample of largest Ly-alpha nebulosities at z ~ 2. These nebulae reside in extremely massive overdensities and associated with groups of QSOs and strong Lyman alpha absorption. With sizes = 200 - 500 kpc, they represent direct imaging of gas extending into the CGM/IGM. Our unique dataset reveal a sample of extremely extended Lyman alpha emission and can be used to study how massive galaxies are fueled by gas from the densest part of the IGM, and how IGM gets enriched.

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Sebastiano Cantalupo

A 3D View of the Circumgalactic Medium in Fluorescent Ly-Alpha Emission

Presenter: Sebastiano Cantalupo, ETH Zurich

         Deep Ly-alpha narrow-band imaging on Keck and Integral Field Spectroscopy with VLT/MUSE around bright quasars is providing us a completely new window for the study of the high-redshift Universe: using quasars and bright galaxies as external “sources of illumination”, we are now finally able to directly map in fluorescent Ly-alpha emission and at high spatial resolution the circumgalactic medium of bright galaxies, as well as intergalactic filaments extending up to several hundred of kpc. In this talk, I will review our observational campaigns for this emission with a particular focus on the latest results obtained with the MUSE integral-field-spectrograph on VLT. These observations are challenging our current theoretical understanding of structure formation based on cosmological simulations, suggesting that a large amount of “cold" and dense gaseous “clumps" should be present around high-redshift galaxies. In the second part of the talk, I will present our first attempts to advance our theoretical and numerical understanding of the formation of these structures as traced by the intergalactic Ly-alpha emission and discuss the consequences for cosmic structure formation.

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Seok-Jun Chang (Poster)

A Basic Monte Carlo Study of Polarization of Lyα Rayleigh Scattered in the Early Universe.

Presenter: Seok-Jun Chang, Sejong University
Additional Authors: Hee-Won Lee, Yujin Yang


         In a medium with a high H~I column density, far UV photons near Lyα or Lyα photon significantly shifted through Doppler effect can be optically thick with respect to Rayleigh scattering. The relevant astrophysical situations include Lyα photons from Lyman Alpha Blobs and broad Lyα emission in active galactic nuclei. Depending on the geometry of the scattering medium these Rayleigh scattered far UV photons near Lyα are expected to be strongly polarized. We investigate polarized radiative transfer of Rayleigh scattered Lyman alpha using a Monte Carlo technique. Basic scattering geometry is adopted including slabs and cylindrical shells with a range of H~I column densities. It is found that a significant degree of linear polarization is expected from Lyα with a moderate Rayleigh scattering optical depth. We also find that polarization direction may change as Rayleigh scattering optical depth sharply increases toward Lyα center. In this poster presentation, we discuss basic mechanism of polarization development of Rayleigh scattered Lyα.

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Henry Childs

The Utility of Lyman-Alpha Emission Lines as a Probe of Interactions Between High Redshift Galaxies & their Environments

Presenter: Henry Childs, University of Warwick
Additional Authors: Dr. Elizabeth Stanway

         Observational limitations mean the best window for finding high redshift outflow markers is in the rest-UV. It has been proposed that rest-UV morphology correlates with Lyman alpha spectral properties and so may provide a proxy for the detection of galaxy outflows. This would have the advantage of making large samples of archival data accessible for studies of the interactions between the young massive stellar populations in early galaxies and their nearby circumgalactic and intergalactic media. However observational uncertainties may compromise this analysis in many cases. The initial work was performed with HST and Keck data - amongst the highest quality and signal to noise of all high redshift datasets. In this study we explore whether the correlation between morphological asymmetry and Lyman-alpha skewness (both hypothesised outflow indicators) holds at lower instrumental resolution and detection signal-to-noise and thus whether the methodology can be extended throughout the archive. We model these effects, and others such as skyline removal, on the parameter recovery of skewed Gaussian emission lines. Unsurprisingly we find a strong bias in results at lower resolutions and high skew values, as-well as substantial uncertainties resulting from the masking of skylines. We present analysis of a range of existing data sets (including sources from FORS2 and DEIMOS) and attempt to reconstruct the recovered initial emission line parameters. We also investigate the possibilities of recovering outflow indicators from line emission with future instruments like JWST and the E-ELT.

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Robin Ciardullo

The Ly-Alpha Escape Fraction at 1.90 < z < 2.35

Presenter: Robin Ciardullo, Penn State University

         The combination of near-IR grism spectroscopy from the Hubble Space Telescope and ground-based Ly-alpha data are a powerful way of exploring the systematics of Ly-alpha escape from high-redshift star-forming galaxies. We summarize the results of an analysis which used the prototype VIRUS spectrograph from the HETDEX pilot survey and WF3/G141 grism observations of COSMOS and GOODS-N to measure the overall Ly-alpha escape fraction of the 1.90 < z < 2.35 universe. We then preview what we may expect to measure in the near future with the combination of HETDEX, on-going HST grism programs, and future EUCLID and WFIRST observations.

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Matthew Cornachione

Morphology & Substructure of Gravitationally Lensed Lyman-Alpha Emitters at 2 < z < 3 from the BOSS Emission-Line Lens Survey (BELLS)

Presenter: Matthew Cornachione, University of Utah
Additional Authors: Adam Bolton, Yiping Shu, Antonio Montero-Dorta, Zheng Zheng


         In this study we examine the morphology of 17 gravitationally lensed Lyman-alpha emitters (LAEs) selected from the spectroscopic database of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Observation by the Hubble Space Telescope (HST) coupled with strong gravitational lensing allows us to resolve these high redshift (2 < z < 3) LAEs on scales of ~100pc. These LAEs are composed of bright clumps in the rest frame UV, in accord with similar studies. Each galaxy includes several, typically 1-10, clumps. We adopt the Sèrsic surface brightness profile to describe each clump and fit for Sèrsic parameters. From best-fit clump parameters we compile galaxy characteristics (number of blobs, quadrupole moment) and clump characteristics (peak brightness, radius, radial distribution, ellipticity). We select and fit probability distributions to each of these characteristics. The distributions will be used in a future study as informed priors when searching for dark matter substructure in the lens galaxies. In the meantime, these distributions provide a window into LAE morphology at smaller scales than achieved in direct imaging and complement other lensing studies.

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Rupert Croft

Intensity Mapping & the Forest

Presenter: Rupert Croft, Carnegie Mellon

         The Lyman-alpha forest was the first spectral intensity map of a continuous cosmological field. I will show how synergies exist between mapping of Lyman-alpha emission and the forest, and how different cross-correlation techniques can be used to make a complete census of Lyman-alpha emission. I will also explore how weak gravitational lensing of Lyman-alpha emission and forest intensity maps can be used to probe the foreground mass distribution of the Universe in a similar fashion to CMB lensing.

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Mark Dijkstra

Exploring the Lyα-LyC Connection

Presenter: Mark Dijkstra, University of Oslo

         The escape of ionizing Lyman continuum (LyC) photons that low-HI-column density sightlines exist. The presence of these sightline also promote escape of Lyα. We therefore expect Lyα and LyC escape fractions to be correlated. This is important: there is increasingly observational evidence that Lyα escapes more easily from UV-faint galaxies. The connection between Lyα and LyC escape then implies that UV faint galaxies contribute more to the ionizing background than implied by the faint-end slope of the UV-luminosity function. I will discuss observational tests of the Lyα-LyC connection, incl. the Lyα spectral line profile and the presence of extended Lyα, UV continuum and Ha halos around star forming galaxies.

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Alyssa Drake

A MUSE View of the HUDF: the Lyα Luminosity Function out to z ~ 6.5

Presenter: Alyssa Drake, CRAL - Lyon
Additional Authors: Bruno Guiderdoni, Jeremy Blaizot, Johan Richard, Takuya Hashimoto, Thibault Garel, Hanae Inami, Floriane Leclercq, Joe Lewis, Roland Bacon & the MUSE consortium


         I will present first results on the Lyα luminosity function in the Hubble Ultra Deep Field (HUDF), using a large, homogeneous, sample of over 600 LAEs selected through blind spectroscopy from MUSE at 3.0 < z < 6.5. The unprecedented power of MUSE to simultaneously detect and spectroscopically identify galaxies has revealed extended Lyα emission around almost every LAE in the sample, allowing us to incorporate the effect of extended halos on total Lyα fluxes and hence on the luminosity function. These data probe further down the Lyα luminosity function than ever before, reaching luminosities of log L ≈ 41.2 erg s−1, and reliably constraining the faint end slope, α, at high redshift, as well as allowing us to assess the evolution of the Lyα luminosity function between z ∼ 3.0 and z ∼ 6.5. I will present our results from this ground-breaking survey and make comparisons to the literature.

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Marius B. Eide

From Blobs to Galaxies & Clouds: the Polarization of Lyα Holds the Key

Presenter: Marius B. Eide, Max Planck Institute for Astrophysics
Additional Authors: Max Gronke, Mark Dijkstra

         Lyman alpha photons (Lyα) remains a powerful probe of the high-redshift universe. During their escape from the source, they experience many scattering events which shape the emergent observables. This makes it contain information not only about the source, but also about the nearby environment. However, different scattering geometries does not always translate to distinguishable observables. An additional Lyα property is needed to break such degeneracies. We have implemented the quantum mechanical description of polarization by Ahn, Lee and Lee (2002) into the Monte Carlo radiative transfer code tlac, and generalized it to cover arbitrary source geometries and dynamics. We show examples of how the polarization of Lyα can disentangle otherwise indistinguishable observables, and even shed light on the geometries of point sources.

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Steven Finkelstein

HETDEX: Discovering One Million LAEs at the Peak of Cosmic Star Formation

Presenter: Steven Finkelstein, UT Austin

         I will introduce the Hobby Eberly Telescope Dark Energy Experiment (HETDEX), just getting underway now at McDonald Observatory in West Texas. HETDEX will study the evolution of the energy density of the dark energy component of our universe by measuring the bispectrum of galaxies at 1.9 < z < 3.5. This probes the spatial correlation of galaxies, which is dependent on the composition of the universe at that epoch, therefore constraining whether the data demand an evolution of dark energy component from today to a time 10 Gyr into the past. Of interest for this meeting is the fact that HETDEX will use Lyman alpha emitting galaxies (LAEs) as its structure tracer, *spectroscopically* discovering one million LAEs over 450°2 (over two fields), all located at the epoch of peak cosmic star formation. I will introduce the HETDEX project, including an update on the status of our instrument VIRUS and the wide-field upgrade to the Hobby Eberly Telescope, as well as a discussion of the survey. I will discuss the wide range of ways in which HETDEX will allow a deeper understanding of LAEs, including the study of the evolution of the Lyman alpha luminosity function, EW distribution, etc., with a finely spaced redshift sampling. Finally, I will discuss how the insights gained on Lyman alpha escape will allow us to better use these galaxies as tools to probe the end of reionization.

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Sofia Gallego

Constraints on the Cosmic Web Lyman α Emission Around z = 3.5 Galaxies Using Galaxy-Pair Stacking

Presenter: Sofia Gallego, ETH Zurich
Additional Authors: Sebastiano Cantalupo, Simon Lilly, Raffaella Marino, Gabriele Pezzulli, Ann-Christine Vossberg & MUSE Collaboration


         We analyse the MUSE deep field cubes in search for intergalactic filaments connecting pairs of Lyman alpha emitting galaxies (LAEs) and fluorescently illuminated by the cosmic UV background. We select 278 LAEs in the HDFS and UDF catalogues between 2.6 < z < 4, from which we take a sample of 323 pairs with a comoving distance 0.5 < d < 20 cMpc. From this sample we extract sub-cubes around LAEs centered on the peaks of the Lyman alpha emission, applying a coordinate transformation to get coordinates relative to the neighbor LAE. We perform a selective stacking of these galaxy pairs dividing the sample according to the redshift, the spatial and the physical separation of the sources, their luminosity and the number of close neighbors. If filaments are aligned with galaxy pairs, as suggested by cosmological simulations, our stacking analysis should significantly increase the probability of detecting the large scale structure of the Universe in fluorescent emission. Our current results provide no detection at an intergalactic scale, but allow us to put a very stringent upper limit on both the physical properties of the intergalactic filaments and the value of the cosmic UV background at high-redshift. At a circumgalactic scale of ~40 kpc, we found evidence for oriented emission towards the neighbor at a 2 sigma level, with respect to random orientations.

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Henry Gebhardt

Optimizing the Information from HETDEX: Cross-Correlation Diagnostics for Contamination in Emission Line Surveys

Presenter: Henry Gebhardt, Penn State
Additional Authors: Donghui Jeong


         HETDEX (Hobby-Eberly Telescope Dark Energy eXperiment) will detect ~800000 Lyman-alpha emitters to be used as a probe of thelarge-scale structure. The sample of Lyman-alpha emitters will be contaminated with low-redshift interlopers such as [O~II] ~3727-emitters due to the low-resolution (R~700) of the spectrographs. Measuring the contamination fraction, in this case, is essential for the cosmological analysis from the catalogue. We will present a novel method of contamination diagnostics that exploits the shape of the auto- and cross-correlations in C-space to measure the contamination fraction. We include redshift-space distortion and lensing magnification, and show that this method allows to measure the contamination fraction to ~0.1% for the HETDEX survey. This technique will also be useful for other future emission line surveys such as eBOSS, WFIRST, SPHEREx, and Euclid, to mention a few.

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Max Grönke

Shells, Clumps & Cloudlets: Subgrid Models of Lyα Radiative Transfer

Presenter: Max Grönke, Institute for Theoretical Astrophysics, University of Oslo
Additional Authors: Mark Dijkstra, Michael McCourt, & S. Peng Oh


         Lyman-alpha spectra potentially contain unique information on physical properties of high-redshift galaxies. However, extracting this information is still challenging. Theorists have therefore resorted to simplified models of this process. One commonly used subgrid-model is the "shell-model", which is highly successful in reproducing observed Lyα spectra. Why this model can reproduce the complex scattering process through the multiphase interstellar-medium is still unclear. I will address this question by contrasting the shell-model with other subgrid-model which consist of neutral clumps embedded within an ionized medium. I focus on the different spectral shapes and what we might learn from this regarding the shell-model.

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Caryl Gronwall

Cosmic Variance in the Physical Properties of Ly-alpha Emitting Galaxies at z = 2.1 & z = 3.1

Presenter: Caryl Gronwall, Pennsylvania State University

         We have used the Mosaic camera of the CTIO 4-m telescope to conduct a deep, narrow- band survey of Ly-alpha Emitting Galaxies (LAEs) over the redshift ranges 3.10 < z < 3.13 and 2.04 < z < 2.08 in two 0.3 square degree fields, one centered on the Extended Hubble Deep Field South and the other on SDSS 1030+05. These data, combined with our previous surveys of the Extended Chandra Deep Field South, give us a total survey volume of 400,000 Mpc3 in 2.06 and 500,000 Mpc3 at 3.1 which has been surveyed down to monochromatic line luminosities of log(L) ~42.3 ergs/s. We analyze the samples of Ly-alpha emitters found in the surveys, and present their luminosity, equivalent width, and color distributions as well as internal extinction and star formation rate. We also use these samples to search for diffuse Ly-alpha halos around LAEs at these redshifts. Most importantly, we use the information provided by our three survey fields to investigate the effect that cosmic variance has on these properties and on measurements of their evolution.

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Siddhartha Gurung López

Impact of Radiative Transfer on the Lyman-Alpha Emitters Clustering

Presenter: Siddhartha Gurung López, CEFCA
Additional Authors: A. Orsi , S. Bonoli


         In the next few years several surveys, such as HETDEX, will use Lyman alpha emitters ( LAEs ) as dark matter tracers in order to study cosmology. Nevertheless the clustering of LAEs might have non-gravitational components since Lyman alpha photons suffer resonant scattering which change the observability of LAEs. We design a realistic model where we take into account the radiative transfer of these photons inside and outside galaxies. By one hand, inside galaxies we use a radiative transfer Monte Carlo code which provides the escape fraction of Lyman alpha photons and the line shape for every galaxy. By the other hand, we also compute the radiative transfer of the intergalactic medium (IGM) taking into account not only the density field, but also the velocity and ionizing radiation fields. In order to fix some free parameters we perform a fit to the observed Lyman alpha luminosity function at several redshifts. At the end the clustering that we predict is a convolution of the dark mater , velocity , ionizing radiation fields and the galaxy properties as the observed one. As in previous works we find significant differences in the Lyman alpha emitters clustering when include the radiative transfer that can mislead future surveys.

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Alex Hagen

Physical Properties of z ~ 2 Lyman-Alpha Emitters & their Use as Tracers of the Star Forming Galaxy Population

Presenter: Alex Hagen, Pennsylvania State University
Additional Authors: Robin Ciardullo, Caryl Gronwall, Joanna Bridge, Henry Gebhardt, Gregory Zeimann, & the HETDEX Team


         Lyman-alpha emitting galaxies (LAEs) provide a unique way to sample low-mass galaxies at high redshift, and are complementary to various photometric selection techniques that generally identify massive high-redshift galaxies. We discuss the physical and morphological properties of z~2 LAEs found photometrically in narrow-band studies and spectroscopically via the HETDEX Pilot Survey. We use spectral energy distribution (SED) fitting of broad-band photometry and morphological analyses of HST rest-frame UV and optical imaging to show that LAEs exhibit a wide range of physical properties. We find that z~2 LAEs extend over a range of 2.5 dex in stellar mass, that Lyman-alpha luminosity is not correlated with stellar mass, and that not all LAEs are dust-poor objects. Furthermore, when we compare the properties of our LAEs to those of z~2 galaxies selected via their their rest-frame optical emission lines, we find no significant differences between the two samples. This suggests that LAEs are simply pulled from the epoch’s general star forming galaxy population. Finally, we comment on the potential of HETDEX for transformative studies of LAEs and the general z~2 population

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Agnar Hall (Poster)

Characterizing the Large-Scale Environments of Giant Lyα Blobs: How Often Do Blobs Reside in Overdensities?

Presenter: Agnar Hall, New Mexico State University
Additional Authors: Moire Prescott


         Recently, evidence has been mounting that giant Lyman alpha (Lyα) nebulae, or "blobs," at high redshift are coincident with regions of galaxy overdensity and likely the progenitors of galaxy groups. While individual Lyα blobs have been found to reside in overdense regions, determining the relationship between Lyα blobs and overdensities in an unbiased way requires studying the galaxy density within Lyα blobs found without knowledge of their environments, as was done by Prescott et al. 2008 which demonstrated that one such blob was nonetheless located in an overdense region. Using Hubble Space Telescope (HST) imaging, we build upon this work and explore the environments of three more systematically-selected blobs at 1.5 < z < 2.5. Comparing the total surface density of galaxies in a region centered on the blob to the average surface density of galaxies in the field, we find that all three blobs display a significant overdensity. After narrowing down which galaxies are most likely to be associated with each Lyα blob, we confirm that the raw overdensities persist and find evidence of a luminosity gap in at least one of the three systems studied, hinting that mergers between the largest member galaxies may have already begin to occur. These results suggest that Lyα blobs may very well be statistically overdense and therefore offer new insight into the early phases of galaxy group and cluster formation.

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Cai-Na Hao

A Census of Low-Mass Star-Forming Galaxies at z ~ 2 via Deep Surveys for Lyman-Alpha Emitters

Presenter: Cai-Na Hao, Tianjin Normal University, P. R. China

         Cosmic star formation rate density peaks at redshift 2~3. At this important epoch, detailed knowledge of massive galaxies have been obtained. However, information on z~2 galaxies with lower stellar mass is still fragmentary. We study the properties of low-mass star-forming galaxies via deep narrow-band surveys for Lyman-alpha Emitters (LAEs) at z~2.23. We observed the COSMOS and ECDF-S fields using our customized narrow-band filter N393 with the Megacam at the Magellan II telescope. The surveys reach a 5σ limiting magnitude of 26 mag within a 3" circular aperture in diameter. Our Lyα luminosity function is consistent with that based on more than 3000 LAEs at similar redshifts, in favor of the steep faint-end slope of -1.75. We find that the majority of our LAEs are located above the extrapolated line of the star-formation main sequence. Two-point correlation function analysis yields a median dark matter halo mass of log(Mh/M) = 11.3±0.3 and bias factor of 1.54±0.2, which suggests that our LAEs will evolve into 1.0-2.5L* galaxies in the local Universe. The stellar-mass-to-halo-mass ratio of our LAEs is lower than model predictions by a factor of 3-30, implying that these low-mass LAEs have not fully assembled their stars, being at the early stage of galaxy formation.

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Santosh Harish (Poster)

Lyman Alpha Fraction of LBGs at z = 4-6

Presenter: Santosh Harish, Arizona State University
Additional Authors: Sangeeta Malhotra, James Rhoads, Lise Christensen, Vithal Tilvi, John Pharo, and Steven Finkelstein

         No abstract submitted.

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Matthew Hayes

Direct in Indirect Observations of Atomic Gas in Lyman-Alpha Agnostic Galaxies

Presenter: Matthew Hayes, Stockholm University
Additional Authors: LARS team (especially J.M. Cannon)


         The Ly-alpha throughput of galaxies’ ISM/CGM is regulated by atomic hydrogen. Unfortunately HI is usually studied with absorption line spectroscopy, which may reveal a biased picture because the observations are prone to line-of-sight effects, and interpretation is further complicated by the use of low ionization metals as proxy species. In this talk I will present the only set of direct observations of the HI envelopes of low-z ( < 0.2) galaxies with Ly-alpha data, which have been obtained in the 21 cm hyperfine transition of HI under major campaigns (~500 hours) at the JVLA and GMRT. I will present HI masses, atomic gas mass fractions, and 21 cm spectral profiles for 34 galaxies, and HI velocity fields obtained at ~6 arcsec resolution for a subset.The sample is the extended LARS sample (eLARS), which is complete with Ly- alpha and UV imaging and spectroscopy from HST. eLARS galaxies were selected as analogues of high-z galaxies, with no prior Ly-alpha information; thus it is very diverse in its Ly-alpha properties and spans from high EW emitting systems to damped absorbers. In this talk I will contrast the Ly-alpha observables {luminosity, EW, Ly-alpha/H-alpha, escape fraction, line profile} with both directly and indirectly measured properties of the atomic medium. This will include the total HI reservoir, velocity dispersion, and mass fraction from radio data, and clumping and line-of-sight kinematics from UV spectra. This will reveal the dependence of Ly-alpha emission on both the large- and small-scale properties of the atomic medium. In a handful of resolved case-studies I will show how Ly-alpha prefers to escape from regions of low column density.

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Alaina Henry

JWST/NIRSpec Multi-Object Spectroscopy Planning Workshop

Presenter: Alaina Henry, STScI

         The era of JWST is fast approaching. At the time of this SnowCLAW meeting, Early Release Proposals will be due in a mere five months. While a new space telescope will lead to revolutionary discoveries, it will also require the astronomical community to grapple with new instruments, systems, and user tools. Indeed, the details pertaining to JWST proposal planning and submission represent, in some cases, significant departures from HST's business-as-usual. This reality is particularly true for NIRSpec, as the first slitted multi-object spectrometer in space. As the JWST/NIRSpec proposal planning deputy at STScI, I propose to present an overview of the NIRSpec multi-object spectroscopy planning process, along with a workshop presentation to guide conference attendees through slit-mask design. If desired, I can also demo the new JWST exposure time calculator, helpdesk system, or online ocumentation. Given the empahsis on spectroscopy among the anticipated conference attendees, information and training on NIRSpec will be relevant and highly valuable.

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Edmund Christian Herenz

Recombination Lines from Circum Galactic Environments

Presenter: Edmund Christian Herenz, Stockholm University

         Circum galactic gas reservoirs play a crucial role in galaxy formation. The unprecedented sensitivity of the MUSE integral field spectrograph allows for studies of the circum galactic medium (CGM) using recombination emission lines: At high-redshifts the CGM can be mapped via Lyman alpha emission, while at low redshifts we can use rest-frame optical emission lines. In my talk I will show observational results from the local Lyman alpha reference sample that establish a link between Lyman alpha and Balmer alpha radiation fields. I will then discuss possible mechanisms to produce Lyman alpha emission from the CGM, so called Lyman alpha haloes. In the following I address how neglecting these haloes in Lyman alpha luminosity function determinations leads to a possible underestimate of the number density of faint Lyman alpha emitting galaxies. I will conclude my talk by showing first results from MUSE observations of an extremely low metallicity local star-burst galaxy (SBS 0335-052E), where we were able to detect a low-surface brightness halo in rest-frame optical lines.

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Anne Jaskot

Lyman-Alpha at High Ionization: New Insights from the Green Peas

Presenter: Anne Jaskot, Smith College
Additional Authors: Sally Oey, Anne Verhamme, Ivana Orlitova


         As the only known population of Lyman continuum (LyC) leaking starbursts at low redshift, the Green Pea galaxies can provide key insights into the properties that affect LyC and Lyman-alpha escape. We have obtained HST COS spectra of Ly-alpha in 13 extreme Green Peas, which include the most highly ionized starbursts at low redshift. We present initial measurements of Ly-alpha strengths, Ly-alpha profile shapes, and low and high ionization absorption lines for these unusual galaxies. With this sample, we assess the relationship between Ly-alpha emission, LyC optical depth, and high nebular ionization and discuss which properties may be conducive to LyC and Ly-alpha escape.

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Linhua Jiang

A Magellan M2FS Spectroscopic Survey of Galaxies at 5.6 < z < 7

Presenter: Linhua Jiang, Peking University

         Here we will introduce our on-going program that uses Magellan M2FS to spectroscopically identify a large number galaxy candidatges at 5.6 < z < 7. M2FS is a fiber-fed, multi-object (256 fibers) spectrograph on the Magellan Clay telescope. With a large field of view (0.5 degrees in diameter), M2FS is very efficient to identify relatively bright high-redshift galaxies. The fields that we selected are well-studied deep fields such as COSMOS and SXDS. They have deep optical imaging data in a series of broad and narrow bands that allow us to efficiently select LAEs at z = 5.7 and 6.6, and LBGs at 5.6 < z < 7. When the program completes, it will cover a total of about four square degrees. The new sample will be used to study physical properties of high-redshift galaxies and their implications to cosmic reionization. So far we have observed about two square degrees, and we will briefly present some preliminary results.

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Intae Jung

Constraining the End of Reionization with Deep Lyman-Alpha Spectroscopy

Presenter: Intae Jung, The University of Texas at Austin
Additional Authors: Steve Finkelstein, Rachael Livermore, Rebecca Larson


         An immediately accessible method for studying the intergalactic medium in the reionization era is to measure the equivalent width distribution of Lyman-alpha emission from continuum-selected galaxies with follow-up spectroscopy. To search for Lyman-alpha emission from galaxies at z = 5.5-8.2, we are performing ultra-deep spectroscopic observations of candidate galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. We utilize data from the DEIMOS (optical) and MOSFIRE (near-infrared) spectrographs on the Keck 10-meter telescopes, ensuring the comprehensive wavelength coverage of Lyman-alpha emission at z ~ 6-8. We have a total of 1220 hours of spectroscopic integration of galaxies at z > 6: 620 hours for 189 galaxies with DEIMOS and 600 hours for 85 galaxies with MOSFIRE with the additional optical spectroscopic data of our sample galaxies in the GOODS-S field from VLT VANDELS survey. The Lyman-alpha fraction, the ratio of galaxies with detected Lyman-alpha emission to the number of all candidate galaxies observed, is directly measured with the completeness test of our dataset by constructing detailed simulations of mock emission lines, which consider observational conditions (e.g., observational depth, wavelength coverage, and sky emission) and the probability distribution function of galaxy photometric redshifts. We will present a robust measure of the distribution of the Lyman-alpha emission equivalent widths in four redshift bins (z ~ 6.5, 7.0, 7.5, and 8.0), determining robust upper limits on the Lyman-alpha emission.

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Koki Kakiichi

Joint Analysis of Lyman-Alpha Emitting Galaxies & QSO Absorption Spectra

Presenter: Koki Kakiichi, University College London

         Using Lyman alpha emission and absorption together, the spectroscopic survey of Lyman alpha emitting galaxies in high-redshift QSO fields over 2 < z < 7 provides a direct probe of reionization and CGM. I present a new method that connects Lyman alpha forest - galaxy cross correlations, Lyman alpha emission line profiles, and Lyman alpha halos to effectively interpret such surveys. I also present a pilot galaxy survey in the z~6 QSO field to demonstrate the potential to constrain reionization.

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Satoshi Kikuta

AGN Environments & Feedback to Neighboring Galaxies at z~5

Presenter: Satoshi Kikuta, National Astronomical Observatory of Japan

         Active galactic nuclei (AGNs) in the high-redshift Universe are thought to reside in overdense regions of galaxies. However, recent works provide mixed results, partly due to the use of different observational techniques and possibly radiative feedback from AGN. To address more robustly whether AGN environments are rich and whether AGN feedback is indeed strong enough to suppress formation of neighboring galaxies, we conducted deep and wide-field imaging observations with the Suprime-Cam on the Subaru telescope and searched for Lyman-alpha emitters (LAEs) around two QSOs (luminous type 1 AGNs) at z ~ 4.9 and a radio galaxy (RG, a radio-loud type 2 AGN) at z ~ 4.5 by using narrow-band filters together with broad-band filters. This method can detect LAEs from much narrower redshift range (Δz ~ 0.1) than the Lyman-break technique (Δz ~ 1). In QSO fields, we also obtained additional broad-band images to select Lyman-break galaxies (LBGs) at z ~ 5 for comparison. We constructed photometric sample of 243 LAEs and 140 LBGs in total. A wide field of view (34' x27' ) of the Suprime-Cam enabled us to probe these galaxies in the immediate vicinities of the QSOs and RG and in the blank fields simultaneously and compare various properties of them in a consistent manner. In all fields, the number densities of LAE around the QSOs and RG are consistent with or lower than those in blank fields as opposed to the naive expectation that they should reside in overdensities. Moreover, we find no clear sign of feedback even in the faintest luminosity bin (down to log LLyα = 41.8). Our results suggest that high-redshift AGNs are not always associated with overdensity of galaxies, not due to radiative feedback.

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Takashi Kojima

First Direct Te Method Determinations of Gas-Phase Metal Abundances & Ionization Parameters for High-z LAEs

Presenter: Takashi Kojima, The University of Tokyo
Additional Authors: Masami Ouchi, Kimihiko Nakajima, Takatoshi Shibuya, Yuichi Harikane, & Yoshiaki Ono


         We present inter-stellar medium (ISM) properties of LAEs that are, for the first time, determined by the direct electron temperature (Te) method. Our sample consists of five typical LAEs at z = 1.7-2.3 with log M*/Mo = 8-10 and EWrest(Lyα) = 30-160A (Kojima et al. 2016) revealed by deep optical and near-infrared spectroscopy. All of the five LAEs have significant detections of OIII]1661,1666 doublet that is an indicator of Te. Correcting for the dust extinction in OIII], [OII]3727, and [OIII]5007 doublets with Balmer decrements of Ha/Hb, we have obtained Te = 1.3-1.4x104 K, gas phase metallicity 12+log(O/H) = 8.05-8.14, and ionization parameter qion = 8.1-8.2 cm/s with a typical error of ~10%. Our reliable approach of the direct Te method confirms the sub-solar metallicity and the very high ionization parameter of typical LAEs, which are previously claimed by independent strong line methods with unknown systematics (e.g. Finkelstein et al. 2012, Nakajima & Ouchi 2014, Erb et al. 2016). We compare the ISM properties of LAEs to those of LBGs with EWrest(Lyα)~0 and the similar M* and SFR based on the direct Te method with a stacked spectrum, and discuss the state of ISM producing strong Lyα emission.

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Andrey Kravtsov

The Size - Virial Relation of Galaxies & its Evolution with Time

Presenter: Andrey Kravtsov, University of Chicago

         I will show that sizes of observed galaxies (from dwarfs to largest ellipticals) at z~0 exhibit a nearly linear correlation with virial masses of their host halos. I will present previous results (Kravtsov 2013) using heterogeneous sample of galaxies and new results (Kravtsov, in prep.) based on the uniform sample of the SDSS galaxies with homogeneous improved photometry and size measurements by Meert et al. (2015). I will also review the current evidence that a similar linear relation holds at higher redshifts, including the Lyman Break Galaxies at z~3-6 and a theoretical interpretation of the relation and its evolution.

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Haruka Kusakabe

Mass Assembly Efficiency of LAEs at z ~ 2: Stellar & Halo Properties

Presenter: Haruka Kusakabe, he University of Tokyo
Additional Authors: Kazuhiro Shimasaku, Kimihiko Nakajima, Masami Ouchi, Ryosuke Goto, Takuya Hashimoto, Akira Konno, Yuichi Harikane, Yoshiaki Ono, John Silverman


         Narrow band Lyα emission surveys are useful to construct a statistical sample of faint low-mass galaxies at high redshifts. Guaita et al. 2010 estimated the halo masses of Lyα emitters (LAEs) at z~2 to be 1011-1012 M (b = 1.8±0.3). Since their stellar masses are estimated to be ~108-109 M (Guaita et al. 2011), it seems that their stellar-to-halo mass ratio (SHMR) lies a little below an extrapolation of the average relation (Behroozi et al. 2013). However, the sample size of the previous study is ~250 and their survey area is ~0.3°2, so one of challenges is to reduce uncertainties of the SHMR. No other observational study goes down to halo masses of 1011 M with estimation of SHMR at z~2. In this work, we select ~2400 LAEs using narrow band NB387 (5σ 26.4 mag) in four deep survey fields (SXDS, COSMOS, GOODS-S and GOODS-N) over 1°2 (Nakajima et al. 2012) and derive their dark matter halo masses from clustering analysis and stellar properties from SED fitting. We find that the average dark matter halo mass over the four field is estimated to be ~1010-1011 M (b = 1.3±0.2) with a wide distribution due to cosmic variance larger than the statistical errors. Sub-sample analyses find no significant dependence of dark matter halo mass on either Lyα luminosity or Lyα equivalent width. Our LAEs in SXDS and COSMOS fields lie above an extrapolation of the Behroozi relation with stellar masses of ~109 M. In addition, since the sub-sample analyses also find that our LAEs have as wide as a 2 dex range of stellar mass, there is the possibility that the dark matter halo mass distribution is also similarly wide. We will discuss star formation activities and efficiencies of LAEs. We will also introduce our future plan using an on-going large-area HSC survey of LAEs.

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Rebecca Larson

A Blind Search for Lyman-Alpha Emission from Galaxies at z = 6-8 with Deep HST Grism Spectra

Presenter: Rebecca Larson, University of Texas at Austin
Additional Authors: Steven L. Finkelstein, Norbert Pirzkal, Vithal Tilvi, Intae Jung, Sangeeta Malhotra, James Rhoads


         This project aims to detect Ly-α emission lines from z = 6-8 galaxies to probe the ionization state of the intergalactic medium (IGM) during the epoch of reionization. We use extremely deep data from the Faint Infrared Grism Survey (FIGS; PI: Malhotra) which is currently the most sensitive G102 Grism survey, targeting the high-redshift galaxies that were discovered in the CANDELS GOODS fields (Finkelstein et al. 2015). This data set has already proven to be successful as one of these candidates, at redshift z = 7.51, has been observed to have Ly-α emission detectable with the HST Grism (Tilvi et al 2016). The FIGS data uses five separate roll-angles of HST in an effort to reduce the overall contamination effects of nearby galaxies. We have created a method that accounts for and removes the contamination from surrounding galaxies, and also removes any residual continuum emission from each individual spectrum. We then utilize an MCMC routine to blindly search for significant emission lines in all position angles simultaneously. We have found several z < 7 candidates which, if confirmed, will significantly increase the number of confirmed galaxies in this epoch. The coarse spectral resolution of the G102 Grism prevents us from measuring the expected asymmetric profile of the Ly-α emission line, so we have proposed for follow-up observations of our objects with ground based facilities.

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Peter Laursen

Chasing Lyman α Emitting Galaxies at z = 8.8

Presenter: Peter Laursen, Institute of Theoretical Astrophysics, University of Oslo
Additional Authors: Johan P. U. Fynbo, Bo Milvang-Jensen, Alexei O. Razoumov, Jesper Sommer-Larsen, Johannes Zabl


         UltraVISTA is an ongoing ~1 deg² NIR survey, one of the aims of which is to find Lyman α emitters (LAEs) at z = 8.8, at the verge of the Epoch of Reionization. While galaxies are known to exist at this redshift, the luminosity function (LF) of LAEs is still not established, and roughly halfway through the survey no LAEs have yet been detected. Instead of extrapolating lower-redshift LFs, we have taken a more ab initio approach; combining theoretical halo mass function with high-resolution hydrodynamical simulations, as well as a radiative transfer of first ionizing UV radiation and subsequently Lyman α, we predict the (discouraging) number of galaxies that we can expect to detect in such a survey.

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Floriane Leclercq

Lyman-Alpha Haloes Around Individual High-Redshift Galaxies Within the MUSE Deep Fields

Presenter: Floriane Leclercq, Centre de Recherche Astrophysique de Lyon
Additional Authors: R. Bacon & The MUSE Collaboration

         Probing the circum-galactic medium represents an important challenge for understanding how galaxies form and evolve. Lyman alpha emission through scattering by neutral hydrogen allows the circum-galactic gas to be observed as a Lyman alpha halo around galaxies. Previous studies, forced to employ stacking analyses because of sensitivity limitations, already showed that Lyman alpha emission is statistically more spatially extended than the UV stellar continuum emission from galaxy counterparts. The significant increase in sensitivity of the Multi-Unit Spectrometer Explorer (MUSE) allows, for the first time, to probe the CGM by the detections of spatially extended emission around individual Lyman alpha emitters (LAEs) at high redshift. We have performed observations that constrain both the spatial extent and morphology of Lyman alpha haloes. A first study presented in Wisotzki et al. (2016) confirms the existence of Lyman alpha haloes around 21 individual star-forming galaxies at z = 3-6 in the Hubble Deep Field South (HDFS). This represents a significant advance over previous stacking analyses which could not prove that Lyman alpha haloes are ubiquitous around LAEs. A second study (Leclercq et al, in prep) extends the sample, using the wider Hubble Ultra Deep Field (UDF). We observed haloes around ~200 galaxies reinforcing the idea that halo is a general property of LAEs. Within this study, we characterized the haloes properties (size, flux, shape) and looked at their relations with respect to general Lyman alpha properties (flux, EW, line profiles, etc) and UV characteristics of host galaxies (magnitude, size, etc). In this talk, I will present results of this last study of Lyman alpha haloes from the UDF field.

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Hee-Won Lee

Asymmetric Deviation of the Cross Section from the Lorentzian Around Ly Alpha

Presenter: Hee-Won Lee, Sejong University

         Reliable radiative transfer of Lyα should be based on exact atomic physics invoking time-dependent second order perturbation theory. The result is summarized by the Kramers-Heisenberg formula, according to whic infinitely many p-states of hydrogen participate in the cross section in the form of weightes sum with the weight inversely proportional to the difference of the photon energy and that of the p-state. Near Lyα line center, the cross section is dominantly contributed by the 2p-state leading to the well-known Lorentzian profile. However, far from the line center, Lorentzian is inappropriate due to nonnegligible contributions from the other p-states. In particular, the cross section deviates from Lorentzian in such an asymmetric way that the cross section is larger in the red part than in the blue part. In this talk, the deviation of the cross section from the Lorentzian function is illustrated and observational ramifications are discussed.

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Kyoung-Soo Lee

The Diverse Sizes of Lyman-Alpha Halos around Normal Star-Forming Galaxies

Presenter: Kyoung-Soo Lee, Purdue University
Additional Authors: Rui Xue


         We report diverse sizes of Lyman Alpha Halos (LAHs) measured for normal star-forming galaxies at high redshift. Based on ~1400 galaxies residing in field and dense protocluster environments, we investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties such as UV luminosity, Lyα luminosity and equivalent widths. The average LAH scalelength, measured for galaxies selected as Lyman Alpha Emitters, is modest at 5-6 kpc (physical); the most UV-luminous galaxies have more extended halos (8-9 kpc). Our analysis largely rules out the presence of very large LAHs around UV-luminous protocluster member galaxies as previously reported based on a similarly significant high-redshift protocluster system. Based on the observed trends of LAH sizes with galaxy parameters, combined with the measured average radial profile of our sample galaxies, we speculate that i) LAHs are primarily powered by central star formation: namely, Lyα photons produced therein escape the interstellar medium and subsequently scatter through the circumgalactic medium (CGM); and ii) the physical conditions of the CGM change with halo mass and/or star formation rates.

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Xiangcheng Ma

Escape Fraction of Lyα & LyC Photons from the FIRE Simulation

Presenter: Xiangcheng Ma, Caltech

         I will present a novel suite of high-resolution cosmological zoom-in simulations of high-redshift galaxies at the epoch of reionization, taking advantage of the realistic models of the ISM, star formation, and stellar feedback from the FIRE project. These simulations resolve the formation and disruption of individual star-forming clouds, which allow us to track the propagation and escape of Lyman-alpha/LyC photons with post-processing radiative transfer calculations. I will discuss three important issues regarding the escape fraction of Lyα/LyC photons and their contributions to reionization: (1) why the ionizing photons are difficult to escape the galaxy, (2) why it is important to include binarity in stellar populations models, and (3) how the ionizing background affect the neutral gas covering fractions around galaxies at the epoch of reionization. These simulations are also able to predict a number of observable galaxy properties and are ideal for motivating and confronting future observations.

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Ramesh Mainali

Evidence for a Hard Ionizing Spectrum from a z = 6.11 Stellar Population

Presenter: Ramesh Mainali, University of Arizona
Additional Authors: Juna A. Kollmeier, Daniel P. Stark, Robert A. Simcoe, Greg Walth, Andrew B. Newmann


         I will present the Magellan/FIRE detection of highly-ionized CIV 1550 and OIII] 1666 in a deep infrared spectrum of the z = 6.11 gravitationally lensed low mass Lyman-alpha emitter. No corresponding emission is detected at the expected location of HeII 1640. The upper limit on HeII paired with detection of OIII] and CIV constrains possible ionization scenarios. The data require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher HeII flux. The conclusions based on ratios of metal line detections to Helium non-detection are strengthened if the gas metallicity is low. This adds to the growing handful of reionization-era Lyman-alpha emitters with UV emission line ratios distinct from the general z = 2-3 population, in a way that suggests hard ionizing spectra that do not necessarily originate in AGN.

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Raffaella Anna Marino

Hunting for the Dark Phases of Galaxy Formation with MUSE

Presenter: Raffaella Anna Marino, Institute for Astronomy, ETH Zurich, Switzerland
Additional Authors: Simon Lilly, Sebastiano Cantalupo, Elena Borisova, Sofia Gallego & the MUSE GTO collaboration


         Theoretical models suggest that the early phases of galaxies formation should involve an epoch when galaxies are gas rich and inefficient at forming stars: a dark galaxy phase. Here, I will present new results on the search for these dark galaxies at high redshift (z~3) obtained from the analysis of different MUSE deep fields part of the Guaranteed Time of Observation program. In particular, we take advantage of the quasar induced, fluorescent Lyman alpha emission to study and detect these otherwise invisible objects to our optical telescopes. On the basis of the few pioneering works from the literature, we already know that dark galaxies appear to be compact, gas-rich, and very inefficient at forming stars but the current sample is very limited. Thanks to the unprecedent capabilities of the MUSE instrument, we are now able to provide a more complete census of fluorescently illuminated dark galaxies as well as to analyze and characterize the main properties of these intriguing objects with a unique spatial and spectral resolution.

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Christopher Martin

Cosmic Web Imager Observations of Circum-Galactic & Circum-QSO Medium Emission at High Redshift

Presenter: Christopher Martin, Caltech

         I describe recent results from the Palomar Cosmic Web Imager (PCWI). These include the discovery of filamentary Lyman alpha emission and a giant (> 120 kpc) protogalactic disk illuminated by a nearby QSO, filamentary emission and a large rotating spiral inflow structure near a second QSO, and filamentary emission around and kinematics in a Lyman Alpha Blob consistent with a large rotating gas structure. The discovery of filamentary and rotating disk-like structures is evidence for cold accretion inflows with significant angular momentum. We also describe future instrumentation exploring IGM emission on the ground and in space.

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Lluís Mas-Ribas

Constraining Star Formation in the Halo of High Redshift Galaxies with Extended Line Emission

Presenter: Lluís Mas-Ribas, University of Oslo
Additional Authors: Mark Dijkstra, Joseph F. Hennawi, Michele Trenti, Rieko Momose, Masami Ouchi


         The faint-end slope of the rest-frame UV luminosity function is steepening towards high-redshift, implying that low-luminosity galaxies account for an increasingly large fraction of the overall galaxy population. Direct studies of theses faint galaxies at high-redshift is extremely challenging. We present a new method to constrain their abundance, and possibly even their contribution to the ionizing background, using extended Lyα and other line emission around more massive/luminous galaxies. We discuss the detectability of these faint emission line halos with future facilities such as JWST.

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Lluís Mas-Ribas (Poster)

The Mean Metal-line Absorption Spectrum of DLAs from BOSS

Presenter: Lluís Mas-Ribas, University of Oslo
Additional Authors: Jordi Miralda-Escudé, Andreu Arinyo-i-Prats, Ignasi Pérez-Ràfols, Pasquier Noterdaeme, Patrick Petitjean, Jian Ge & Donald G. York


         Damped Lyman Alpha absorption systems (DLAs) are defined to have hydrogen column densities NHI > 2 × 1020 cm−2, where the gas in the core is self-shielded against the external ionizing radiation (Wolfe et al. 2005). DLAs constitute an important reservoir of gas for star formation and the derived metallicities are generally low, distributed over a broad range of 10−3 to 10−1Z, on average declining with redshift. Using data from the Baryon Oscillation Spectroscopic Survey (Dawson et al. 2013) of the Sloan Digital Sky Survey-III (Eisenstein et al. 2011) DR12 we calculate the mean metal-line absorption spectrum by averaging over ~ 27000 systems which allows for the detection of faint metal absorption lines, several of them within the Lyman Alpha forest. We study the dependence of the equivalent widths of any line on the hydrogen column density and we propose a theoretical model to correct for line saturation and to estimate the column densities of low-ionization species.

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Jorryt Matthee

Spectroscopic Studies of Luminous Lyman-Alpha Emitters in the Epoch of Reionisation

Presenter: Jorryt Matthee, Leiden Observatory
Additional Authors: David Sobral, Sergio Santos, Huub Röttgering


         I will present results from our wide-field narrow-band surveys with Subaru and the VLT to search for galaxies through their Lyman-alpha emission line at z~6-8. We have found that luminous Lyα emitters at z = 6.6 are much more common than previously thought, with implications for reionisation. Our best studied galaxy, COSMOS Redshift 7 (CR7), has spectroscopic evidence for a very hot source (105 K) in an extremely low metallicity gas (Z < 3x10-3 Z), which has sparked a lot of theoretical investigations into its nature. I will focus specifically on the ongoing follow-up of CR7 with ALMA and HST and on the follow-up of similar LAEs at z = 5.7 and z = 6.6 through HST imaging and X-SHOOTER spectroscopy.

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Jens Melinder

Lyman-Alpha Escape from Nearby Galaxies - the Lyman-Alpha Reference Sample

Presenter: Jens Melinder, Stockholm University
Additional Authors: Göran Östlin, Matthew Hayes, Angela Adamo, Andreas Sandberg, Thøger Rivera-Thorsen, John Cannon, Christian Herenz, & the LARS team


         The Lyman alpha reference sample (LARS) is a major multiwavelength imaging and spectroscopic campaign of local normal star-forming galaxies, UV-luminous starburst systems, and luminous infrared galaxies using HST and ground-based telescopes. The aim of this survey is to probe what physical conditions and processes regulate the emission of Ly alpha radiation on local and global galactic scales. The fact that Ly alpha is a resonant line makes it optically thick even at relatively low neutral hydrogen column densities, this means that the radiative transport of Ly alpha photons through galaxies is a complex problem where the structure, kinematics and dust content, and neutral hydrogen content of the interstellar medium all contribute to the process. In this talk I will present the current status of the project including: unique HST Ly alpha maps and FUV spectroscopy of 44 galaxies within the LARS sample, HI observations with GBA and VLA for a subset of the sample, IFU spectroscopy using CAHA/PMAS and VLT/MUSE for a subset of the sample. The first published results of the LARS survey, for 14 of the galaxies, revealed that when Ly alpha manages to escape it does so in the form of diffuse scattering halos. I will show that the addition of ~30 more galaxies to this sample reinforces this conclusion, and that Lyman alpha escape is strongly affected both by neutral gas and dust content of the galaxies.

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Kimihiko Nakajima

A Hard Ionizing Spectrum in Ly-Alpha Emitters with Intense [OIII] Emission

Presenter: Kimihiko Nakajima, European Southern Observatory

         We present the diagnostic nebular emission lines [OIII], [OII] and H-beta for a sample of Ly-alpha emitting galaxies (LAEs) at z = 3-4. In comparison with similar measurements of other surveys, we demonstrate that LAEs have much larger [OIII]/[OII] line ratios and larger xiion - the number of Lyman continuum photons per UV luminosity - than those seen in Lyman break galaxies. I will discuss how a hard ionizing radiation field, a low metallicity, and potentially a high escape fraction of ionizing photons can explain such intense line emission by using photoionization models, and present how further observations could confirm these possibilities.

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Desika Narayanan

The Connection Between Massive Galaxies & Lyman-Alpha Blobs

Presenter: Desika Narayanan, University of Florida
Additional Authors: Jim Geach, Mark Dijkstra, Lluis Mas, Romeel Dave, & others


         The origin of high-redshift lyman alpha blobs is at present uncertain. In an effort to understand the origin of LABs, we have run a series of high-resolution cosmological zoom galaxy evolution simulations. We have coupled these simulations with both dust radiative transfer calculations (so that we know what the galaxies would 'look' like), and Lyman Alpha radiative transfer calculations. We find that, owing to extended star formation, Lyα photons can escape from the central galaxy and scatter off of neutral gas in the CGM within the parent halo. Much of this gas is associated with satellite systems. We show quantitatively a possible link between massive galaxy evolution and LAB formation, and highlight some recent observations by our group to confirm this potential scenario.

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Shiyu Nie

The Link Between Circumgalactic Medium & Shell Model Constraints from Lyman-Alpha Emitting Galaxies in Hydrodynamic Simulations

Presenter: Shiyu Nie, University of Utah
Additional Authors: Zheng Zheng, Raphael Sadoun, Renyue Cen


         As Lyman-alpha photons are scattered by neutral hydrogen atoms surrounding the galaxies, Lyman-alpha emission encodes information about the neutral hydrogen distribution around galaxies. The expanding shell model motivated by galactic outflow has successfully reproduced the observed Lyman-alpha spectra from Lyman-alpha emitting galaxies. The simplified geometry of the shell model and the complex gas distribution around galaxies, however, make it necessary to investigate what we can learn about the circumgalactic media (CGM) from the shell model constraints. By applying the shell model to fit the Lyman-alpha spectra derived from radiative transfer modeling of galaxies in hydrodynamic simulations, we study the relation between the shell model parameters and the CGM properties. We find that in general the constraints in velocity, temperature, and column density of neutral hydrogen from the shell model occupy a small region in the parameter space, compared to the much broader distribution of neutral gas in the simulated galaxies. While each parameter constrained in the shell model falls into the range of corresponding distribution in the simulated galaxies, the joint distribution of the parameters do not match well with that in the simulation. We discuss the implications of our results.

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Masami Ouchi

First Year Results of the Subaru 30°2 Survey for Lyα Emitters at z~2-7

Presenter: Masami Ouchi, University of Tokyo

         I present progresses of our Subaru Hyper Suprime-Cam (HSC) surveyfor Lyα emitters (LAEs) at z~2-7 in a total area of 30°2, and overview the first-year results. The data of the first-year resultsallow us to obtain over 2000 LAEs at z = 6-7 in the sky of 20°2 that are about an order of magnitude larger than previous LAE surveys.Exploiting the z = 6-7 LAE largest sample ever made, we deriveLyα luminosity functions and angular correlation functions. Based onthese statistical measurements, I discuss evolution of low-mass galaxy properties and cosmic reionization that can be probed via the Lyα damping wing absorption of the IGM neutral hydrogen. We identify extremely bright and/or extended Lyα emitters at z~6-7 whose Subaru+Keck optical and near-infrared spectra are taken, and compare the UV nebular line emission properties of our LAEs with those of dropouts at z~6-7. We find interesting IRAC color excess objects, indicative of strong nebular lines, among our LAEs at z~6-7 whose magnitudes are significantly brighter than the known IRAC color excess objects in the HST data. Now we plan to publish the first-year results of the HSC high-z galaxies in 10 papers this spring, 5 of which are based on these Lyα emitter results.

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Lucia Perez (Poster)

Comparison of Clustering Analysis Methods for Lyman-Alpha Emitter-Inhabited Dark Matter Halo Simulations

Presenter: Lucia Perez, Arizona State University

         The void probability function has shown promise as a more sensitive and efficient probe of the large scale structure of the universe as compared to other methods. This work presents comparative measurements of the traditional two-point angular correlation function and the void probability of multiple simulations of LAE-inhabited dark matter halos from the work of Tilvi et al. (2009) across a wide redshift range. These results provide evidence for the VPF as an accurate and significantly less computationally intensive measure of the clustering, as well as evidence for increased clustering of galaxies at higher redshifts.

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Celine Peroux

Physical Properties of the Circum-Galactic Medium from Lyman-Alpha Emission & Absorption

Presenter: Celine Peroux, Laboratoire d'Astrophysique de Marseille

         Studies of the circumgalactic medium are crucial for understanding both the inflows of gas accreting into galaxies and the outflows carrying away the energy and metals generated inside galaxies. A powerful tool to study this so-called "baryon cycle" is provided by the Lyman-alpha transition. While Lyman-alpha emission detection offers the potential to map CGM region, dedicated simulations indicate that the expected fluxes will be faint. To reach the lower density gas, it is thus essential to complement emission studies with absorption lines observed in background quasar spectra. Integral fieldspectroscopy (IFS) has proven an efficient way to combine emission and absorption physical properties of the gas flows around galaxies, allowing to determine the kinematics and metallicity of the circum-galactic medium.

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Moire Prescott

A Multi-Wavelength View of Lyα Nebulae

Presenter: Moire Prescott, New Mexico State University
Additional Authors: Crystal Martin, Arjun Dey, Iva Momcheva, Gabriel Brammer, Johan Fynbo, Palle Møller


         Using detailed multi-wavelength data, we explore the kinematics, environment, and power source in individual Lyα nebulae. In one system, we find that resonant scattering is disfavored as the dominant explanation for the extended Lyα nebula, and evidence that the nebular gas is rotationally supported. In another, considered to be the best candidate for a Lyα nebulae powered by gravitational cooling, our comprehensive analysis instead argues for a larger role from photoionization by an AGN. Both cases show evidence for overdense environments, supporting the picture of Lyα nebulae as the precursors of galaxy groups.

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Ewald Puchwein

Constraining Reionization with Models of the Visibility of Lyman-Alpha Emitters

Presenter: Ewald Puchwein, KICC & IoA, University of Cambridge
Additional Authors: Tirthankar Roy Choudhury, Martin G. Haehnelt, James S. Bolton


         We use a combination of cosmological hydrodynamical simulations and semi-numerical methods to illuminate the reionization history of the IGM. We confront our models of the visibility of Lyman-alpha emitting galaxies with the latest observational constraints on their abundance and redshift evolution. To match the data we need a late and not too extended reionization history in agreement with recent constraints on the Thomson scattering optical depth towards the CMB.

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James Rhoads

An Upper Limit on the Volume Neutral Fraction at z = 6.5

Presenter: James Rhoads, Arizona State University
Additional Authors: Sangeeta Malhotra


         We present a tight upper limit on the volume filling fraction of neutral intergalactic hydrogen at redshift z = 6.5, based on a new analysis of Lyman alpha galaxy statistics at z = 5.7 and 6.5. We apply the method we proposed in Malhotra & Rhoads 2006, using modern data sets. Because a neutral intergalactic medium (IGM) scatters Lyman alpha photons, each Lyman alpha galaxy we observe at z = 6.5 implies the presence of an ionized region there. The similarity of the z = 6.5 and 5.7 Lyman alpha luminosity functions implies typical sizes of > 15 comoving Mpc for these regions. Combining the volume of the ionized regions with their number density gives a volume-weighted IGM ionization fraction. The best available estimates of key Lyman alpha galaxy population properties imply a neutral fraction xn < 1%. Our Monte Carlo simulations to explore the uncertainties in this estimate show a tail towards less stringent bounds, with 15% of simulations allowing neutral fractions above 15%, and < 1% of simulations allowing neutral fractions above 60%. We close by discussing prospects for improving this test's bounds at z = 6.5 and for applying the test at higher redshifts using new, large surveys for z > = 7 Lyman alpha.

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Raphael Sadoun

Radiative Transfer Modeling of Lyman-Alpha Emitters as a Probe of Reionization

Presenter: Raphael Sadoun, University of Utah

         Reionization is the last major phase transition in the Universe during which the Intergalactic medium (IGM) changed from a fully neutral to highly ionized state. As Lyman-alpha emission from star-forming galaxies is sensitive to the neutral gas environment, Lyman-alpha emitters (LAEs) are among the few observational probes to the reionization process. I will present results from radiative transfer calculations aimed at modeling the Lyman-alpha properties of LAEs during reionization. I will first show how the expected variation in the ionizing UV background level during reionization can account for the observed evolution in the fraction of Lyman-alpha emitters among dropout galaxies at z~6-7. I will also describe our work on the statistical properties of LAEs at high-z from radiative transfer modeling of galaxies in high-resolution cosmological reionization simulations. As the simulation outputs are chosen to match the targeted redshifts of upcoming narrowband LAE surveys, our study provides an important tool to help interpreting future observations.

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Claudia Scarlata

A High Space Density of Luminous Lyman-Alpha Emitters at Z ~ 6.5

Presenter: Claudia Scarlata, University of Minnesota

         I will present the results of a systematic search for Lyman-alpha emitters (LAEs) at 6<z<7.6 using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our survey covers a volume ~ 8x105 Mpc3, comparable to many of the narrowband surveys despite their larger area coverage. We identify two LAEs at z ~ 6.4 which are among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. These LAEs reside in Mpc-scale ionized bubbles that allow the Ly-alpha photons to redshift out of resonance before encountering the neutral IGM. Based on the observed constraints, we conclude that the observed LAEs alone are not sufficient to ionize their surrounding bubbles.

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Kasper Schmidt

MUSE-Wide: A (Not So) Shallow Survey Mapping 1000 Lyman-Alpha Emitters at 3 < z < 6 with 100 MUSE Pointings

Presenter: Kasper Schmidt, Leibniz-Institut für Astrophysik Potsdam (AIP)
Additional Authors: The MUSE Collaboration


         The MUSE-Wide survey is building a 100 arcmin2 mosaic in the CDF-S and COSMOS fields. From the 60 pointings analyzed so far, the ongoing survey has detected more than 600 Lyman alpha emitting galaxies (LAEs) at redshifts between 3 and 6. Hence, the MUSE-Wide IFU data are supplying an unprecedented sample of spectroscopic LAEs ideal for studying the physical properties of LAEs at high redshift. Taking advantage of the synergy between the MUSE-Wide data, which reaches flux sensitivities of 1e-17 erg/s/cm2, and the vast amount of ancillary archival multi-wavelength imaging available in the CDF-S and COSMOS fields, we are studying the demographics of the MUSE-Wide LAEs. I will present the MUSE-Wide survey and the first results from our exploration of the Lyman alpha emitting galaxy population when the Universe was less than 2 Gyr old.

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Kasper Schmidt (Poster)

The z > 5.5 Universe Seen Through a Magnifying GLASS

Presenter: Kasper Schmidt, Leibniz-Institut für Astrophysik Potsdam (AIP)
Additional Authors: The GLASS Collaboration


         The Grism Lens-Amplified Survey from Space (GLASS) is a large HST program which targeted 10 massive galaxy clusters all with extensive HST imaging from CLASH and the Hubble Frontier Fields Initiative. GLASS has obtained 140 orbits of near-infrared WFC3 spatially resolved spectroscopy of thousands of galaxies behind the 10 galaxy clusters. These data probe galaxy evolution during the first few billion years after Big Bang. In this poster, I will present GLASS and the first data release of the project, as well as a selection of our most recent results including a census of Lyman-alpha emission at z>6 and the study of a highly ionizing multiply imaged source at z=6.11 with both Lyman-alpha and CIV emission detected in the GLASS data.

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Aaron Smith

Lyman-Alpha Radiation Pressure

Presenter: Aaron Smith, University of Texas at Austin
Additional Authors: Volker Bromm & Avi Loeb


         Radiation from the first stars and galaxies initiated the dramatic phase transition marking an end to the cosmic dark ages. The emission and absorption signatures from the Lyman-alpha transition of neutral hydrogen have been indispensable in extending the observational frontier for high-redshift galaxies into the epoch of reionization. Lyman-alpha radiative transfer provides clues about the processes leading to Lyman-alpha escape from individual galaxies and the subsequent transmission through the intergalactic medium. Cosmological simulations incorporating Lyman-alpha radiative transfer enhance our understanding of fundamental physics by supplying the inferred spectra and feedback on the gas. We discuss the dynamical impact of Lyman-alpha radiation pressure on galaxy formation throughout cosmic reionization with the first fully coupled Lyman-alpha radiation-hydrodynamics simulations. We self-consistently follow the chemistry, cooling, self-gravity, and ionizing radiation in protogalaxies and find that Lyman-alpha radiation pressure turns out to be dynamically important in several spherically symmetric simulations. As a case in point we apply our model to the COSMOS redshift 7 (CR7) galaxy at z = 6.6, which exhibits a +160 km/s velocity offset between the Lyman-alpha and HeII line peaks. We find that a massive black hole with a nonthermal Compton-thick spectrum is able to reproduce the observed Lyman-alpha signatures as a result of higher photon trapping and longer potential lifetime. We conclude with a general discussion of the role of Lyman-alpha radiation pressure in galaxy formation by considering simulations that cover the expected range of halo and source properties.

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David Sobral

Lyα & LyC Photons Struggle to Escape Typical Star-Forming Galaxies, but not Lyα Emitters

Presenter: David Sobral, Lancaster University
Additional Authors: Jorryt Matthee


         I will present new results from our CALYMHA (CAlibrating LYMan-alpha with H-alpha) survey, a large, matched Lyα-Halpha survey to robustly establish how Lyman-alpha (Lyα) and Lyman-continuum (LyC) photons escape from typical star-forming galaxies at high-redshift. We find that large (~40 kpc) Lyα halos are ubiquitous in typical star-forming galaxies with a range of properties, a consequence of the typical escape fraction of Lyα photons being typically below a few percent, but increasing at larger radii. However, the escape fractions of Lyα selected sources are significantly higher and typically ~30%. Lyα escape fractions depend on dust extinction, UV slope and star-formation rate. Lyα EW seems to be an excellent predictor of both Lyα and LyC escape fractions, with the relation between the Lyα escape fraction (measured from Lyα-Ha) and Lyα EW remaining impressively constant over at least 11-12 Gyrs. I will conclude by discussing how Lyα emitters may be important/significant LyC leakers and how selecting on Lyα emission (irrespectively of the nature of Lyα emitters) may be the most unbiased and complete way to select LyC leakers and the sources with the highest production of ionising photons per UV luminosity.

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Daniel Stark

UV Metal Line Emission in z > 6 Lyman-Alpha Emitters

Presenter: Daniel Stark, University of Arizona

         No abstract submitted

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V. Tilvi

Evolution of Lyα Fraction: A Fast & Early Reionization?

Presenter: V. Tilvi, Arizona State University

         Redshift evolution of Lyman-alpha (Lyα) fraction (fraction of galaxies with strong Lyα emission) provides a simple yet a powerful probe of the neutral hydrogen in the intergalactic medium (IGM), and hence a practical probe of epoch of reionization. Recent spectroscopic observations suggest that the Lyα fraction (especially for fainter galaxies) drops significantly at z > 7, suggesting that the reionization is still in progress at z > 7. However, this conclusion is based on the observations taken by ground-based slit-spectrographs, which have recently been found to underestimate emission line fluxes, by up to a factor of ~5. We are currently investigating this and our preliminary results suggest that if the ground-based fluxes are in fact underestimated, our conclusions about the neutral hydrogen fraction in the IGM are affected. If confirmed, this will suggest that the reionization happened much more quickly, and at higher redshift than the current estimate.

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Ryan Trainor

Lyα Emission Across Galaxy Populations

Presenter: Ryan Trainor, UC Berkeley

         Although Lyα emission is produced generically in star-forming galaxies, the many physical processes that modulate Lyα production, transmission, and escape cause observable Lyα properties to vary strongly across galaxy populations. However, measurement of the Lyα emission alone is typically insufficient to discriminate among these diverse effects. Using results from the on-going Keck Baryonic Structure Survey (KBSS) and KBSS-Lyα survey, I will describe how combined rest-UV and rest-optical spectroscopy can constrain the physics of Lyα production and escape over a wide range of galaxy properties and populations.

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Hideki Umehata

ALMA Reveals Strong [CII] Emission in a Galaxy Embedded in a Giant Lyman-Alpha Blob at z = 3.1

Presenter: Hideki Umehata, The Open University of Japan

         We report the result from observations conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) to detect [CII] 158 um fine structure line emission from galaxies embedded in one of the most spectacular Lyman-alpha blobs (LABs) at z = 3.1, SSA22-LAB1. Of three dusty star-forming galaxies previously discovered by ALMA 860 um dust continuum survey toward SSA22-LAB1, we detected the [CII] line from one, LAB1-ALMA3 at z = 3.0993+/-0.0004. No line emission was detected, associated with the other ALMA continuum sources or from three rest-frame UV/optical selected zspec~3.1 galaxies within the field of view. For LAB1-ALMA3, we find relatively bright [CII] emission compared to the infrared luminosity (L[CII]/L[CII]) and an extremely high [CII] 158 um and [NII] 205 um emission line ratio (L[CII]/L[NII] > 55). The relatively strong [CII] emission may be caused by abundant photodissociation regions and sub-solar metallicity, or by shock heating. The origin of the unusually strong [CII] emission could be causally related to the location within the giant LAB, although the relationship between extended Lyman-alpha emission and ISM conditions of associated galaxies is yet to be understand.

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Anne Verhamme

Escape of Lyman-Alpha & Lyman Continuum Photons from Galaxies

Presenter: Anne Verhamme, Geneva University

         To test if galaxies are the sources of cosmic reionization, and understand the physical conditions and mechanisms which regulate the escape of ionizing photons from primeval galaxies, indirect diagnostics for Lyman continuum (LyC, λ < 912Å) leakage must be used, since direct observation at z ~ 6 is prevented by IGM attenuation. I will present theoretical predictions for the Lyα spectral shape of Lyman Continuum Emitters (Verhamme+15), and their observational confirmation (Verhamme+17). I will then show new results on the spatial vs spectral distributions of Lyα radiation from galaxies and comparison with MUSE and VUDS observations. Finally, I will show first results on Lyα radiation transfer in hydrodynamics simulations of virtual Lyman Continuum Emitters.

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Lutz Wisotzki

The Covering Fraction of Ly-Alpha Haloes at z > 3 from MUSE

Presenter: Lutz Wisotzki, Leibniz Institute for Astrophysics Potsdam (AIP)
Additional Authors: The MUSE Collaboration

         We present a follow-up study to our recent discovery of ubiquitous extended Ly-alpha emission around individual normal galaxies at z > 3 from ultra-deep MUSE observations (Wisotzki et al. 2016). While that paper - as well as the new large study of Lyα haloes in the Hubble UDF by Leclercq et al, also submitted to SnowCLAW - focuses on relatively Lyα-bright and isolated objects, we now investigate the demographics of Lyα haloes over the entire known population of faint high-redshift galaxies inside the MUSE field of view. In addition to revealing many more individually detected haloes we perform a stacking analysis of the Lyα signal, pushing the surface brightness detection limit down to ~1e-20 erg s-1 cm-2. At this level a large fraction of the field of view is actually covered with Lyα emission from redshifts 3 < z < 6, and we present a spectacular colour image visualising the "Sky in Ly-alpha". We evaluate the projected covering fraction of Lyα emission as a function of surface brightness, redshift, and of the magnitude of the central galaxy.

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Isak Wold

Do High Equivalent Width LAEs Exist in the Local Universe? Insights from a Flux-Limited GALEX LAE sample at z ~ 0.3

Presenter: Isak Wold, UT-Austin
Additional Authors: Steve Finkelstein, Amy Barger


         Observational surveys of Lyα emitters (LAEs) have proven to be an efficient method to identify and study large numbers of galaxies over a wide redshift range. To understand what types of galaxies are selected in LAE surveys - and how this evolves with redshift - it is important to establish a low-redshift reference sample that can be directly compared to high-redshift samples. The lowest redshift where a direct Lyα survey is currently possible is at a redshift of z~0.3 via the Galaxy Evolution Explorer (GALEX ) FUV grism data. Using the z~0.3 GALEX sample as an anchor point, it has been suggested that at low redshifts high equivalent width (EW) LAEs become less prevalent and that the amount of escaping Lyα emission declines rapidly. A number of explanations for these trends have been suggested including increasing dust content, increasing neutral column density, and/or increasing metallicity of star-forming galaxies at lower redshifts. However, the published z~0.3 GALEX sample is pre-selected from bright NUV objects. Thus, objects with strong Lyα emission but faint continuum (high-EW LAEs) could be missed. In this talk, I will present my efforts to re-reduce the deepest archival GALEX FUV grism data and obtain a sample that is not biased against high-EW LAEs. I will discuss the implications of this new sample on the evolutionary trends listed above.

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Huan Yang

Studying Lyα Escape & Lyα sizes in a Statistical Sample of Green Pea Galaxies

Presenter: Huan Yang, Arizona State University
Additional Authors: Sangeeta Malhotra, Max Gronke, James E. Rhoads, Claus Leitherer, Aida Wofford, Tianxing Jiang, Mark Dijkstra, V. Tilvi, Junxian Wang


         I will present our studies of Lyman-alpha escape in a statistical sample of 43 Green Pea galaxies with HST/COS observations. Our sample is four times larger than the previous sample and covers a much more complete range of Green Pea properties. About 2/3 of Green Peas are strong Lyα line emitters with rest-frame Lyα equivalent width > 20 Å. The Lyα profiles of Green Peas are diverse. We studied the dependence of the Lyα escape fraction on many other properties, including the Lyα kinematic features, dust reddening, metallicity, stellar mass, [OIII]/[OII] ratio, size and morphology. We fit an empirical linear relation to predict Lyα escape fraction from the dust extinction and Lyα red peak velocity. This relation can be used to probe the IGM optical depth along the line of sight of each z > 7 Lyα emission line galaxy in the JWST era. Then we studied the spatial profiles of Lyα and UV continuum from their 2D COS spectra. The Lyα emission shows more extended spatial profiles than the UV continuum in most Green Peas. We also compared the Lyα and UV sizes of Green Peas to the sizes of MUSE z = 3 − 6 LAEs.

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Yujin Yang

Polarimetric Survey of Giant Lyman-Alpha Nebulae

Presenter: Yujin Yang, Korea Astronomy and Space Science Institute
Additional Authors: Chang You, Ann Zabludoff, Paul Smith, Eunchong Kim, Buell Jannuzi, Moire K. M. Prescott, Yuichi Matsuda, Myung Gyoon Lee


         I will present first results of our effort to map the polarization of giant Ly-alpha nebulae at high-redshift. Giant Lyα nebulae, or blobs, are extended (~100 kpc), bright clouds of Lyα emitting gas that tend to lie in over-dense regions at z = 2-5. The origin of the Lyα emission remains unknown, but recent theoretical work suggests that measuring the polarization might discriminate among powering mechanisms and constrain the physical state of the extended gas. In this talk, I will present the first narrowband, imaging polarimetry of a radio-loud Lyα nebula, B3 J2330+3927 at z = 3.09, with an embedded AGN. The AGN lies near the blob's Lyα emission peak and its radio lobes align roughly with the blob's major axis. With the MMT/SPOL polarimeter, we map the Lyα polarization in a grid of circular apertures of radius 0.6" (4.4kpc), detecting a significant polarization fraction (P) in nine apertures and achieving strong upper-limits (as low as 2%) elsewhere. P increases from < 2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The detections are distributed asymmetrically, roughly along the nebula's major axis. The polarization angles (theta) are mostly perpendicular to this axis. These results suggest that Lyα photons are produced in the center, instead of arising throughout the nebula itself. We speculate that the lack of polarization detected along the minor axis could be due to strong obscuration from an AGN torus perpendicular to the radio-jet. Or, ionization states and optical depths vary from one axis to the other due to photo-ionization along the jet or its interaction with the IGM.

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Zheng Zheng

Connections Between Anisotropic Gas Distribution & Properties of Lyman-Alpha Emission from Lyman-Alpha Emitting Galaxies

Presenter: Zheng Zheng, University of Utah
Additional Authors: Joshua Wallace, Raphael Sadoun, Renyue Cen


         As Lyman-alpha photons escape from Lyman-alpha emitting galaxies (LAEs), they experience resonant scatterings with neutral hydrogen atoms around galaxies. The anisotropic neutral gas environment naturally leads to anisotropic escape of Lyman-alpha photons. Based on Lyman-alpha radiative transfer calculations, I will present investigations of the anisotropic Lyman-alpha emission with both simple gas cloud models and galaxies in hydrodynamic simulations. In particular, with the simulated galaxies, I will show that the anisotropic gas distribution around galaxies and the corresponding anisotropic Lyman-alpha emission provide an important ingredient in shaping some observed properties of LAEs (e.g., the Lyman-alpha equivalent width distribution). I will also briefly discuss the extended Lyman-alpha emission from the simulated galaxies, which produces a brightness profile in remarkable agreement with that of the observed diffuse Lyman-alpha halos.

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Zhenya Zheng

First Results from the Lyman-Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Galaxy Evolution & Reionization at z ~ 7

Presenter: Zhenya Zheng, Shanghai Astronomical Observatory

         We present the first results from our on-going, the largest narrowband survey project for z ~7 galaxies -- the LAGER project: Lyman Alpha Galaxies in the Epoch of Reionization. With a specially built narrowband filter for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 square-degree COSMOS field. We find 27 high confidence Lyman Alpha Emitter (LAE) candidates at z = 6.9 in the central 2 square-degree region, where DECam and public COSMOS multi-band images exist. Our results support differential evolution in the bright and faint end of the Ly-alpha luminosity function. Our results strongly support the hyprothesis of ionized bubbles in the patchy reionization.

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