Two Local Volume Dwarf Galaxies Discovered in 21 cm Emission: Pisces A
  and B
  We report the discovery of two dwarf galaxies, Pisces A and B, from a blind
21 cm HI search. These were the only two galaxies found via optical imaging and
spectroscopy of 22 HI clouds identified in the GALFA-HI survey as dwarf galaxy
candidates. They have properties consistent with being in the Local Volume
($<10$ Mpc), and one has resolved stellar populations such that it may be on
the outer edge of the Local Group ($\sim 1 \, {\rm Mpc}$ from M31). While the
distance uncertainty makes interpretation ambiguous, these may be among the
faintest starforming galaxies known. Additionally, rough estimates comparing
these galaxies to $\Lambda$CDM dark matter simulations suggest consistency in
number density, implying that dark matter halos likely to host these galaxies
are primarily HI-rich. The galaxies may thus be indicative of a large
population of dwarfs at the limit of detectability that are comparable to the
faint satellites of the Local Group. Because they are outside the influence of
a large dark matter halo to alter their evolution, these galaxies can provide
critical anchors to dwarf galaxy formation models.
