SDSS-IV MaNGA: drivers of stellar metallicity in nearby galaxies

The distribution of stellar metallicities within and across galaxies is an excellent relic of the chemical evolution across cosmic time. We present a detailed analysis of spatially resolved stellar populations based on > 2.6 million spatial bins from 7439 nearby galaxies in the SDSS-IV MaNGA survey. To account for accurate inclination corrections, we derive an equation for morphology dependent determination of galaxy inclinations. Our study goes beyond the well-known global mass-metallicity relation and radial metallicity gradients by providing a statistically sound exploration of local relations between stellar metallicity [Z/H], stellar surface mass density Σ_* and galactocentric distance in the global mass-morphology plane. We find a significant resolved mass density-metallicity relation rΣ_*ZR for galaxies of all types and masses above 10^9.8 M_⊙. Different radial distances make an important contribution to the spread of the relation. Particularly, in low and intermediate mass galaxies, we find that at fixed Σ_* metallicity increases with radius independently of morphology. For high masses, this radial dependence is only observed in high Σ_* regions of spiral galaxies. This result calls for a driver of metallicity, in addition to Σ_* that promotes chemical enrichment in the outer parts of galaxies more strongly than in the inner parts. We discuss gas accretion, outflows, recycling and radial migration as possible scenarios.