Leo P: How Many Metals can a Very Low-Mass, Isolated Galaxy Retain?
  Leo P is a gas-rich dwarf galaxy with an extremely low gas-phase oxygen
abundance (3% solar). The isolated nature of Leo P enables a quantitative
measurement of metals lost solely due to star formation feedback. We present an
inventory of the oxygen atoms in Leo P based on the gas-phase oxygen abundance
measurement, the star formation history, and the chemical enrichment evolution
derived from resolved stellar populations. The star formation history also
provides the total amount of oxygen produced. Overall, Leo P has retained 5 %
of its oxygen; 25% of the retained oxygen is in the stars while 75% is in the
gas phase. This is considerably lower than the 20-25% calculated for massive
galaxies, supporting the trend for less efficient metal retention for lower
mass galaxies. The retention fraction is higher than that calculated for other
alpha elements (Mg, Si, Ca) in dSph Milky Way satellites of similar stellar
mass and metallicity. Accounting only for the oxygen retained in stars, our
results are consistent with those derived for the alpha elements in dSph
galaxies. Thus, under the assumption that the dSph galaxies lost the bulk of
their gas mass through an environmental process such as tidal stripping, the
estimates of retained metal fractions represent underestimates by roughly a
factor of four. Because of its isolation, Leo P provides an important datum for
the fraction of metals lost as a function of galaxy mass due to star formation.
