Gas metallicity distributions in SDSS-IV MaNGA galaxies: what drives gradients and local trends?

TL;DR

This study uses SDSS-IV MaNGA data to analyze how gas metallicity in galaxies depends on local stellar mass density and radius, revealing different dominant factors in various galaxy types and linking these to galaxy evolution processes.

Contribution

It provides new insights into the relative importance of radius and stellar mass density in determining gas metallicity across different galaxy types and environments.

Findings

Radius is more predictive of metallicity in low-mass, extended galaxies.

Density and radius are equally predictive in high-mass, compact galaxies.

Metallicity gradients are mildly influenced by large-scale environment.

Abstract

The gas metallicity distributions across individual galaxies and across galaxy samples can teach us much about how galaxies evolve. Massive galaxies typically possess negative metallicity gradients, and mass and metallicity are tightly correlated on local scales over wide range of galaxy masses; however, the precise origins of such trends remain elusive. Here, we employ data from SDSS-IV MaNGA to explore how gas metallicity depends on local stellar mass density and on galactocentric radius within individual galaxies. We also consider how the strengths of these dependencies vary across the galaxy mass-size plane. We find that radius is more predictive of local metallicity than stellar mass density in extended lower mass galaxies, while we find density and radius to be almost equally predictive in higher-mass and more compact galaxies. Consistent with previous work, we find a mild connection between metallicity gradients and large-scale environment; however, this is insufficient to explain variations in gas metallicity behaviour across the mass-size plane. We argue our results to be consistent with a scenario in which extended galaxies have experienced smooth gas accretion histories, producing negative metallicity gradients over time. We further argue that more compact and more massive systems have experienced increased merging activity that disrupts this process, leading to flatter metallicity gradients and more dominant density-metallicity correlations within individual galaxies.