Hubble Space Telescope Observations of Two Faint Dwarf Satellites of
  Nearby LMC Analogs from MADCASH
  We present a deep Hubble Space Telescope (HST) imaging study of two dwarf
galaxies in the halos of Local Volume Large Magellanic Cloud (LMC) analogs.
These dwarfs were discovered as part of our Subaru+Hyper Suprime-Cam MADCASH
survey: MADCASH-1, which is a satellite of NGC 2403 (D~3.2 Mpc), and MADCASH-2,
a previously unknown dwarf galaxy near NGC 4214 (D~3.0 Mpc). Our HST data reach
>3.5 mag below the tip of the red giant branch (TRGB) of each dwarf, allowing
us to derive their structural parameters and assess their stellar populations.
We measure TRGB distances ($D=3.41^{+0.24}_{-0.23}$ Mpc for MADCASH-1, and
$D=3.00^{+0.13}_{-0.15}$ Mpc for MADCASH-2), and confirm their associations
with their host galaxies. MADCASH-1 is a predominantly old, metal-poor stellar
system (age ~13.5 Gyr, [M/H] ~ -2.0), similar to many Local Group dwarfs.
Modelling of MADCASH-2's CMD suggests that it contains mostly ancient,
metal-poor stars (age ~13.5 Gyr, [M/H] ~ -2.0), but that ~10% of its stellar
mass was formed 1.1--1.5 Gyr ago, and ~1% was formed 400--500 Myr ago. Given
its recent star formation, we search MADCASH-2 for neutral hydrogen using the
Green Bank Telescope, but find no emission and estimate an upper limit on the
HI mass of $<4.8\times10^4 M_{\odot}$. These are the faintest dwarf satellites
known around host galaxies of LMC mass outside the Local Group
($M_{V,\text{MADCASH-1}}=-7.81\pm0.18$, $M_{V,\text{MADCASH-2}}=-9.15\pm0.12$),
and one of them shows signs of recent environmental quenching by its host. Once
the MADCASH survey for faint dwarf satellites is complete, our census will
enable us to test CDM predictions for hierarchical structure formation, and
discover the physical mechanisms by which low-mass hosts influence the
evolution of their satellites.
