Presentation #108.02D in the session Dwarf Galaxies in the Local Group.
The beginning of our Universe continues to elude us with many unanswered questions, some involving the evolutionary histories of the most ancient galaxies — ultra–faint dwarfs (UFDs). Recent optical observation and cosmological simulation advancements, however, opened new opportunities to study these evolutionary histories. For example, ancient stellar populations observed in UFDs suggest that their star formation was suppressed via reionization. Alternatively, most well–studied UFDs have small Galactocentric distances making them consistent with an early accreted population, suggesting quenching took place via environmental processes. To study this possibility, my work utilizes Exploring the Local Volume in Simulations (ELVIS), an N–body simulation suite, to constrain the distribution of infall times for low–mass subhalos likely to host UFDs. We find that environment is unlikely to play a dominant role in quenching their star formation. As the Milky Way (MW) and its satellite system become entrenched in near field cosmology, the need for an accurate estimate of the MW’s dark matter halo mass is critical. Using 6D phase-space information for MW satellites, calculated from Gaia’s early third data release of stellar proper motions, compared to subhalo properties drawn from the Phat ELVIS simulations, we constrain the MW’s dark matter halo mass to be ≅1–1.2×1012 Msun. This preferred host halo mass is largely insensitive to the exclusion of Large Magellanic Cloud (LMC) satellites, galaxy formation threshold changes, and observational completeness variations. My current work constrains chemical abundances for an LMC UFD satellite, Hydrus I. Through abundance trends, we will begin to explore how large scale environments, such as the LMC’s dark matter halo, have impacted UFDs’ evolutionary histories. These mostly unexplored evolutionary histories help refine which UFDs are pristine relics of the first galaxies ever formed, serving as the most optimal cosmic sites to search for signatures of the first stars ever formed.