Ultrafaint Dwarf Galaxies: Smallest Scales Quenching & Predictions

Katy Rodriguez Wimberly (UC Irvine)
Friday, February 7, 2020 - 12:15pm to 1:00pm

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. Most of the well-studied UFDs, however, are within the central half of the
Milky Way dark matter halo, such that they are consistent with a population that was
accreted at early times - therefore potentially quenched via environmental processes.
To study this possibility, we utilize the Exploring the Local Volume in Simulations
(ELVIS) suite of N-body simulations to constrain the distribution of infall times for low-
mass subhalos likely to host the UFDs. For the ultra-faint satellites of the Milky Way
with star formation histories inferred from Hubble Space Telescope imaging, we find
that environment is highly unlikely to play a dominant role in quenching their star
formation. Even when including pre-processing effects, there is a ≲ 0.1% probability
that environmental processes quenched our UFDs early enough to explain their
observed star-formation histories. Instead, we argue for a mass floor in the
effectiveness of satellite quenching at roughly M★ ~105 M⊙, below which star formation
in surviving galaxies is globally suppressed by reionization. Further in the exploration of
our ultra-faint satellites, with the second data release of stellar proper motions from
Gaia, several groups calculated phase space and orbit information. We use this new
dynamic information to compare against the next generation of ELVIS, the Phat ELVIS
simulations. This work in progress suggests that while the N-body simulations with an
embedded disk potential are statistically more representative of the Milky Way system,
the orbits of these lowest-mass satellites are still not well represented. Additionally,
when matching dark matter subhalos to observed galaxies based on current distance,
the cumulative distribution of pericenters point towards a lighter mass Milky Way.


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