Extinguishing the FIRE: environmental quenching of satellite galaxies
  around Milky Way-mass hosts in simulations
  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. Intermediate- to high-mass satellites usually
require $\geq1-2$ pericentre passages ($\approx2.5-5$ Gyr) within a MW-mass
halo to quench. 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 are broadly consistent with the
quiescent fractions of satellites observed in the LG and the SAGA survey,
because the simulation average lies between them and the host-to-host scatter
is large.
