Extinguishing the FIRE: environmental quenching of satellite galaxies around Milky Way-mass hosts in simulations

Abstract

The star formation and gas content of satellite galaxies around the Milky Way (MW) and Andromeda (M31) are depleted relative to more isolated galaxies in the Local Group (LG) at fixed stellar mass. We explore the environmental regulation of gas content and quenching of star formation in $z=0$ galaxies at $M*=10^{5-10}\rm{M}_{\odot}$ around 14 MW-mass hosts from the FIRE-2 simulations. Lower-mass satellites ($M*\lesssim10^7\rm{M}_{\odot}$) are mostly quiescent and higher-mass satellites ($M*\gtrsim10^8\rm{M}_{\odot}$) are mostly star-forming, with intermediate-mass satellites ($M*\approx10^{7-8}\rm{M}_{\odot}$) split roughly equally between quiescent and star-forming. Hosts with more gas in their circumgalactic medium have a higher quiescent fraction of massive satellites ($M*=10^{8-9}\rm{M}_{\odot}$). We find no significant dependence on isolated versus paired (LG-like) host environments, and the quiescent fractions of satellites around MW-mass and LMC-mass hosts from the FIRE-2 simulations are remarkably similar. Environmental effects that lead to quenching can also occur as preprocessing in low-mass groups prior to MW infall. Lower-mass satellites typically quenched before MW infall as central galaxies or rapidly during infall into a low-mass group or a MW-mass galaxy. Most intermediate- to high-mass quiescent satellites have experienced $\geq1-2$ pericentre passages ($\approx2.5-5$ Gyr) within a MW-mass halo. Most galaxies with $M*\gtrsim10^{6.5}\rm{M}_{\odot}$ did not quench before falling into a host, indicating a possible upper mass limit for isolated quenching. The simulations reproduce the average trend in the LG quiescent fraction across the full range of satellite stellar masses. Though the simulations are consistent with the SAGA survey's quiescent fraction at $M*\gtrsim10^8\rm{M}_{\odot}$, they do not generally reproduce SAGA's turnover at lower masses.