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⋆/M⊙) ∼ 9.4 to 11.1 and are offset from the mass–metallicity relation by −0.3 to −0.85dex 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. Subject headings: galaxies: abundances – galaxies: evolution