Dark and luminous satellites of LMC-mass galaxies in the FIRE
  simulations
  Within $\Lambda$CDM, dwarf galaxies like the Large Magellanic Cloud (LMC) are
expected to host numerous dark matter subhalos, several of which should host
faint dwarf companions. Recent Gaia proper motions confirm new members of the
LMC-system in addition to the previously known SMC, including two classical
dwarf galaxies ($M_\ast$ > $10^5$ M$_{\odot}$; Carina and Fornax) as well as
several ultra-faint dwarfs (Car2, Car3, Hor1, and Hyd1). We use the Feedback In
Realistic Environments (FIRE) simulations to study the dark and luminous (down
to ultrafaint masses, $M_\ast$ ~ $6\times10^3$ M$_{\odot}$) substructure
population of isolated LMC-mass hosts ($M_\text{200}$ = $1-3\times10^{11}$
M$_{\odot}$) and place the Gaia + DES results in a cosmological context. By
comparing number counts of subhalos in simulations with and without baryons, we
find that, within 0.2 $r_\text{200}$, LMC-mass hosts deplete ~30% of their
substructure, significantly lower than the ~70% of substructure depleted by
Milky Way (MW) mass hosts. For our highest resolution runs ($m_\text{bary}$ =
880 M$_{\odot}$), ~5-10 subhalos form galaxies with $M_\ast$ > $10^4$
M$_{\odot}$, in agreement with the 7 observationally inferred pre-infall LMC
companions. However, we find steeper simulated luminosity functions than
observed, hinting at observation incompleteness at the faint end. The predicted
DM content for classical satellites in FIRE agrees with observed estimates for
Carina and Fornax, supporting the case for an LMC association. We predict that
tidal stripping within the LMC potential lowers the inner dark matter density
of ultra faint companions of the LMC. Thus, in addition to their orbital
consistency, the low densities of dwarfs Car2, Hyd1, and Hyd2 reinforce their
likelihood of Magellanic association.
