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Christopher Ahn Thesis Defense 05/02/2018

Thesis Defense

Christopher Ahn Wednesday, May 2, 2018 at 11 AM (110 INSCC)

Title: Detecting Supermassive Black Holes in Ultracompact Dwarf Galaxies

One of the most fundamental questions in astronomy to this day remains how galaxies form and evolve. The introduction of cosmological simulations and large scale surveys over the past two decades have started to test formation mechanism theories. While the combination of these powerful tools has confirmed many predictions of the large-scale structure of the Universe, they have also exposed a number of issues on smaller scales, especially in the low-mass galaxy regime. It is unclear whether these issues are associated with the simulations or observational constraints. Therefore, detailed studies of low-mass stellar systems are of vital importance in understanding this conflict. It is the goal of this thesis to provide such information from a special class of objects known as ultracompact dwarf galaxies (UCDs).

UCDs are a class of compact stellar systems intermediate to that of globular clusters and dwarf galaxies. Early interpretations of their origin have ranged from UCDs being the high mass end of the globular cluster distribution to the tidally stripped remnants of dwarf galaxies. Recent analyses have shown that the dynamical mass appears to be systematically elevated when compared to the stellar population estimates, which can be explained by central massive black holes (BH)s making up ~10-15% of the total dynamical mass. In my thesis, I test this hypothesis in two projects searching for central massive BHs in three UCDs with the Jeans Anisotropic Modeling (JAM) and Schwarzschild dynamical modeling methods.

My first project presents the JAM modeling of two Virgo UCDs, VUCD3 and M59cO. Assuming isotropy, I detect central massive BHs in both objects with masses of (4.4-30)+25 x 106 M in VUCD3 and (5.8-28)+25 x 106 M in M59cO. These BHs make up an astonishing ~13% and ~18% of the total dynamical mass for VUCD3 and M59cO, respectively.

My second project presents dynamical modeling using both models, mentioned above, of the most massive UCD, M59-UCD3. The best fit models in the JAM and an axisymmetric Schwarzschild model have BHs between 2.5 and 5.9 million solar masses, while a triaxial Schwarzschild model prefers a solution with no BH. However, models with a BH in each technique provide a better fit to the central VRMS profiles, and thus I estimate the BH mass to be (4.2-2.1)+1.7 x 10 6 M. This central black hole makes up ~2% of the total dynamical mass. These BHs, combined with structural information of each UCD, suggest all three objects are the tidally stripped remnants of 109 - 1010 M galaxies.

Last Updated: 12/21/18