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 _ { \star } / \mbox { M } _ { \odot } ) \sim 9.4 to 11.1 and are offset from the mass–metallicity relation by -0.3 to -0.85 dex in 12 + \log ( \mbox { O } / \mbox { 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 .