Charting Unexplored Dwarf Galaxy Territory With RR Lyrae
  Observational bias against finding Milky Way (MW) dwarf galaxies at low
Galactic latitudes (b < 20 deg) and at low surface brightnesses (fainter than
29 mag arcsec^-2, in the V-band) currently limits our understanding of the
faintest limits of the galaxy luminosity function. This paper is a
proof-of-concept that groups of two or more RR Lyrae stars reveal MW dwarf
galaxies at d > 50 kpc in these unmined regions of parameter space, with only
modest contamination from interloper groups when large halo structures are
excluded. For example, a friends-of-friends (FOF) search with a linking length
of 500 pc could reveal dwarf galaxies more luminous than M_V = -3.2 mag and
with surface brightnesses as faint as 31 mag arcsec^-2 (or even fainter,
depending on RR Lyrae specific frequency). Although existing public RR Lyrae
catalogs are highly incomplete at d > 50 kpc and/or include <1% of the MW
halo's volume, a FOF search reveals two known dwarfs (Bootes I and Sextans) and
two dwarf candidate groups possibly worthy of follow-up. PanSTARRS 1 (PS1) may
catalog RR Lyrae to 100 kpc which would include ~15% of predicted MW dwarf
galaxies. Groups of PS1 RR Lyrae should therefore reveal very low surface
brightness and low Galactic latitude dwarfs within its footprint, if they
exist. With sensitivity to RR Lyrae to d >600 kpc, LSST is the only planned
survey that will be both wide-field and deep enough to use RR Lyrae to
definitively measure the Milky Way's dwarf galaxy census to extremely low
surface brightnesses, and through the Galactic plane.
