Ultrafaint Dwarf Galaxies: Smallest Scales Quenching & Predictions

The predominantly ancient stellar populations observed in the lowest-mass galaxies (i.e. ultra-faint dwarfs - UFDs) suggest that their star formation was suppressed by reionization. The close proximity of the well-studied UFDs, however, implies that they are consistent with a population that was accreted at early times - thus potentially quenched via environmental processes. To study this, we utilize N-body simulations to constrain the distribution of infall times for low-mass subhalos. For the Milky Way’s UFDs with star formation histories (SFHs) inferred from Hubble Space Telescope imaging, we find that environment is highly unlikely ( ≲ 0.1% probability) to play a dominant role in quenching their star formation. Instead, we argue for a mass floor in the effectiveness of satellite quenching at roughly M★ ~105 M⊙, below which star formation is globally suppressed by reionization. Further in the exploration of our ultra-faint satellites, we utilize Gaia-derived orbital kinematics to compare against N-body simulations. This work in progress suggests that when matching dark matter subhalos to observed galaxies based on current distance, the cumulative distribution of velocity components point toward an intermediate mass Milky Way. With the enhanced astrometry capabilities of the Nancy Grace Roman Space Telescope, each of these results can be refined through in depth studies of the faintest galaxies within the Milky Way system