Gas-phase Metallicity as a Diagnostic of the Drivers of Star-formation on Different Spatial Scales

TL;DR

This paper investigates how gas-phase metallicity correlates with star formation rate across different spatial scales, using observations and a theoretical model to understand the physical drivers of star formation variability.

Contribution

It introduces a theoretical framework linking SFR, gas mass, and metallicity variations to inflow rate and SFE, explaining scale-dependent correlations observed in galaxies.

Findings

Galactic scale SFR variations driven by inflow rate changes.

100 pc scale SFR variations driven by star-formation efficiency.

Observed correlations differ between galactic and local scales.

Abstract

We examine the correlations of star formation rate (SFR) and gas-phase metallicity $Z$. We first predict how the SFR, cold gas mass and $Z$ will change with variations in inflow rate or in star-formation efficiency (SFE) in a simple gas-regulator framework. The changes $\Delta {\rm log}$SFR and $\Delta {\rm log} Z$, are found to be negatively (positively) correlated when driving the gas-regulator with time-varying inflow rate (SFE). We then study the correlation of $\Delta {\rm log}$sSFR (specific SFR) and $\Delta {\rm log}$(O/H) from observations, at both $\sim$100 pc and galactic scales, based on two 2-dimensional spectroscopic surveys with different spatial resolutions, MAD and MaNGA. After taking out the overall mass and radial dependences, which may reflect changes in inflow gas metallicity and/or outflow mass-loading, we find that $\Delta {\rm log}$sSFR and $\Delta {\rm log}$(O/H) on galactic are found to be negatively correlated, but $\Delta {\rm log}$sSFR and $\Delta {\rm log}$(O/H) are positively correlated on $\sim$100 pc scales within galaxies. If we assume that the variations across the population reflect temporal variations in individual objects, we conclude that variations in the star formation rate are primarily driven by time-varying inflow at galactic scales, and driven by time-varying SFE at $\sim$100 pc scales. We build a theoretical framework to understand the correlation between SFR, gas mass and metallicity, as well as their variability, which potentially uncovers the relevant physical processes of star formation at different scales.