Outliers from the Mass-Metallicity Relation. II. A Sample of Massive Metal-Poor Galaxies from SDSS

We present a sample of 42 high-mass low-metallicity outliers from the mass-metallicity relation of star-forming galaxies. These galaxies have stellar masses that span log(M _sstarf/M _sun) ~ 9.4 to 11.1 and are offset from the mass-metallicity relation by -0.3 to -0.85 dex in 12 + log(O/H). In general, they are extremely blue, have high star-formation rates for their masses, and are morphologically disturbed. Tidal interactions are expected to induce large-scale gas inflow to the galaxies' central regions, and we find that these galaxies' gas-phase oxygen abundances are consistent with large quantities of low-metallicity gas from large galactocentric radii diluting the central metal-rich gas. We conclude with implications for deducing gas-phase metallicities of individual galaxies based solely on their luminosities, specifically in the case of long gamma-ray burst host galaxies.