Measuring distances to low-luminosity galaxies using surface brightness
  fluctuations
  We present an in-depth study of surface brightness fluctuations (SBFs) in
low-luminosity stellar systems. Using the MIST models, we compute theoretical
predictions for absolute SBF magnitudes in the LSST, HST ACS/WFC, and proposed
Roman Space Telescope filter systems. We compare our calculations to observed
SBF-color relations of systems that span a wide range of age and metallicity.
Consistent with previous studies, we find that single-age population models
show excellent agreement with observations of low-mass galaxies with $0.5
\lesssim g - i \lesssim 0.9$. For bluer galaxies, the observed relation is
better fit by models with composite stellar populations. To study SBF recovery
from low-luminosity systems, we perform detailed image simulations in which we
inject fully populated model galaxies into deep ground-based images from real
observations. Our simulations show that LSST will provide data of sufficient
quality and depth to measure SBF magnitudes with precisions of ${\sim}0.2$-0.5
mag in ultra-faint $\left(\mathrm{10^4 \leq M_\star/M_\odot \leq 10^5}\right)$
and low-mass classical (M$_\star\leq10^7$ M$_\odot$) dwarf galaxies out to
${\sim}4$ Mpc and ${\sim}25$ Mpc, respectively, within the first few years of
its deep-wide-fast survey. Many significant practical challenges and systematic
uncertainties remain, including an irreducible "sampling scatter" in the SBFs
of ultra-faint dwarfs due to their undersampled stellar mass functions. We
nonetheless conclude that SBFs in the new generation of wide-field imaging
surveys have the potential to play a critical role in the efficient
confirmation and characterization of dwarf galaxies in the nearby universe.
