Inflow and outflow properties, not total gas fractions, drive the evolution of the mass-metallicity relation

TL;DR

This study reveals that the evolution of the galaxy mass-metallicity relation from redshift 0 to 3 is primarily driven by inflow and outflow properties, not by changes in gas fractions, providing new insights into galaxy evolution processes.

Contribution

The paper demonstrates that the evolution of the mass-metallicity relation is mainly due to changes in inflow and outflow metallicities and mass loading, challenging previous assumptions about gas fraction influence.

Findings

Gas fraction evolution does not significantly affect the MZR evolution.

Inflow and outflow metallicities, and mass loading, are key drivers of MZR evolution.

The MZR evolution is not due to galaxies moving along a fixed surface in parameter space.

Abstract

Observations show a tight correlation between the stellar mass of galaxies and their gas-phase metallicity (MZR). This relation evolves with redshift, with higher-redshift galaxies being characterized by lower metallicities. Understanding the physical origin of the slope and redshift evolution of the MZR may provide important insight into the physical processes underpinning it: star formation, feedback, and cosmological inflows. While theoretical models ascribe the shape of the MZR to the lower efficiency of galactic outflows in more massive galaxies, what drives its evolution remains an open question. In this letter, we analyze how the MZR evolves over $z=0-3$, combining results from the FIREbox cosmological volume simulation with analytical models. Contrary to a frequent assertion in the literature, we find that the evolution of the gas fraction does not contribute significantly to the redshift evolution of the MZR. Instead, we show that the latter is driven by the redshift-dependence of the inflow metallicity, outflow metallicity, and mass loading factor, whose relative importance depends on stellar mass. These findings also suggest that the evolution of the MZR is not explained by galaxies moving along a fixed surface in the space spanned by stellar mass, gas phase metallicity, and star formation rate.