The suppression of star formation on the smallest scales: what role does environment play?

Abstract

The predominantly ancient stellar populations observed in the lowest mass galaxies (i.e. ultrafaint dwarfs) suggest that their star formation was suppressed by reionization. Most of the well-studied ultra-faint dwarfs, 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 and thus potentially quenched via environmental processes. To study the potential role of environment in suppressing star formation on the smallest scales, we utilize the Exploring the Local Volume in Simulations suite of N-body simulations to constrain the distribution of infall times for low-mass subhaloes likely to host the ultra-faint population. 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 the potential effects of pre-processing, there is a 0.1 per cent probability that environmental processes quenched all of the known ultra-faint dwarfs 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 ∼ 10 5 M , below which star formation in surviving galaxies is globally suppressed by reionization. We predict a large population of quenched ultra-faint dwarfs in the Local Field (1 < R/R vir < 2), with as many as ∼250 to be discovered by future wide-field imaging surveys.

A profile in FIRE: resolving the radial distributions of satellite galaxies in the Local Group with simulations

“…Our results agree with studies that have found that satellite survival depends on host-satellite distance at pericentric passage (e.g. D' Onghia et al 2010;Zhu et al 2016;Sawala et al 2017;Garrison-Kimmel et al 2018b;Nadler et al 2018;Rodriguez Wimberly et al 2019). We note that the destruction that we see is somewhat less extreme than in Garrison-Kimmel et al (2017b), who used two of our baryonic simulations (m12i and m12f) and found no surviving subhalos at z = 0 within ∼20 kpc of the host.…”

Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group

“…If baryonic effects act to create or destroy planes of satellites, then dark matter-only simulations may not be able to wholly capture the theoretical picture of satellite plane formation. The central disk in baryonic simulations tidally destroys satellites, altering their radial profile at small distances from the host (e.g., D'Onghia et al 2010;Sawala et al 2017;Garrison-Kimmel et al 2017;Nadler et al 2018; Kelley et al 2018;Rodriguez Wimberly et al 2019;Samuel et al 2020). This leads the surviving satellites to have more tangentially biased orbits (Garrison-Kimmel et al 2017, 2019a, but these effects do not necessarily imply an effect on planarity.…”

Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V*

“…The radial velocity of TucanaII has been measured (Walker et al 2016), but no spectroscopy is available for the other three systems, so the viability of their association with each other or with the Magellanic Clouds has not been tested. Finding dwarf galaxies that formed with only other dwarfs as their neighbors will enable novel tests of the effects of environment on early galaxy formation and evolution (e.g., D'Onghia & Lake 2008; Wetzel et al 2015;Fillingham et al 2019;Rodriguez Wimberly et al 2019).…”