The Dependence of the Mass-Metallicity Relation on Large Scale
  Environment
  We examine the relation between gas-phase oxygen abundance and stellar
mass---the MZ relation---as a function of the large scale galaxy environment
parameterized by the local density. The dependence of the MZ relation on the
environment is small. The metallicity where the MZ relation saturates and the
slope of the MZ relation are both independent of the local density. The impact
of the large scale environment is completely parameterized by the
anti-correlation between local density and the turnover stellar mass where the
MZ relation begins to saturate. Analytical modeling suggests that the
anti-correlation between the local density and turnover stellar mass is a
consequence of a variation in the gas content of star-forming galaxies. Across
$\sim1$ order of magnitude in local density, the gas content at a fixed stellar
mass varies by $\sim5\%$. Variation of the specific star formation rate with
environment is consistent with this interpretation. At a fixed stellar mass,
galaxies in low density environments have lower metallicities because they are
slightly more gas-rich than galaxies in high density environments. Modeling the
shape of the mass-metallicity relation thus provides an indirect means to probe
subtle variations in the gas content of star-forming galaxies.
