The metallicity's fundamental dependence on both local and global galactic quantities

TL;DR

This study investigates how local and global galactic properties influence gas-phase metallicity in star-forming galaxies, revealing local stellar mass density as the primary factor and highlighting the roles of global galaxy characteristics.

Contribution

It demonstrates that local metallicity depends mainly on stellar mass surface density and global galaxy properties, challenging the idea that gas accretion is the primary driver of metallicity variations.

Findings

Local metallicity primarily depends on stellar mass surface density.

Secondary anti-correlation between metallicity and star formation rate surface density.

Global properties like total stellar mass significantly influence local metallicity.

Abstract

We study the scaling relations between gas-phase metallicity, stellar mass surface density ($\Sigma _*$), star formation rate surface density ($\Sigma _{SFR}$), and molecular gas surface density ($\Sigma_{H_2}$) in local star-forming galaxies on scales of a kpc. We employ optical integral field spectroscopy from the MaNGA survey, and ALMA data for a subset of MaNGA galaxies. We use Partial Correlation Coefficients and Random Forest regression to determine the relative importance of local and global galactic properties in setting the gas-phase metallicity. We find that the local metallicity depends primarily on $\Sigma _*$ (the resolved mass-metallicity relation, rMZR), and has a secondary anti-correlation with $\Sigma _{SFR}$ (i.e. a spatially-resolved version of the 'Fundamental Metallicity Relation', rFMR). We find that $\Sigma_{H_2}$ is less important than $\Sigma_{SFR}$ in determining the local metallicity. This result indicates that gas accretion, resulting in local metallicity dilution and local boosting of star formation, is unlikely to be the primary origin of the rFMR. The local metallicity depends also on the global properties of galaxies. We find a strong dependence on the total stellar mass ($M_*$) and a weaker (inverse) dependence on the total SFR. The global metallicity scaling relations, therefore, do not simply stem out of their resolved counterparts; global properties and processes, such as the global gravitational potential well, galaxy-scale winds and global redistribution/mixing of metals, likely contribute to the local metallicity, in addition to local production and retention.