ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo P. IV.
  Distance Measurement from LBT Optical Imaging
  Leo P is a low-luminosity dwarf galaxy discovered through the blind HI
Arecibo Legacy Fast ALFA (ALFALFA) survey. The HI and follow-up optical
observations have shown that Leo P is a gas-rich dwarf galaxy with both active
star formation and an underlying older population, as well as an extremely low
oxygen abundance. Here, we measure the distance to Leo P by applying the tip of
the red giant branch (TRGB) distance method to photometry of the resolved
stellar population from new Large Binocular Telescope (LBT) V and I band
imaging. We measure a distance modulus of 26.19 (+0.17/-0.50) mag corresponding
to a distance of 1.72 (+0.14/-0.40) Mpc. Although our photometry reaches 3
magnitudes below the TRGB, the sparseness of the red giant branch (RGB) yields
higher uncertainties on the lower limit of the distance. Leo P is outside the
Local Group with a distance and velocity consistent with the local Hubble flow.
While located in a very low-density environment, Leo P lies within ~0.5 Mpc of
a loose association of dwarf galaxies which include NGC 3109, Antlia, Sextans
A, and Sextans B, and 1.1 Mpc away from its next nearest neighbor, Leo A. Leo P
is one of the lowest metallicity star-forming galaxies known in the nearby
universe, comparable in metallicity to I Zw 18 and DDO 68, but with stellar
characteristics similar to dwarf spheriodals (dSphs) in the Local Volume such
as Carina, Sextans, and Leo II. Given its physical properties and isolation,
Leo P may provide an evolutionary link between gas-rich dwarf irregular
galaxies and dSphs that have fallen into a Local Group environment and been
stripped of their gas.
