The metallicity of galactic winds

TL;DR

This paper uses high-resolution simulations to study how galactic winds influence the metallicity evolution of galaxies, revealing that wind properties vary with galaxy mass and impact the mass-metallicity relation.

Contribution

It introduces a detailed simulation approach to model galactic winds and their effect on metallicity, providing new insights into galaxy evolution models.

Findings

Winds from massive galaxies are hotter and more enriched.

The gas fraction controls the metallicity and explains the mass-metallicity relation.

Predicted metallicity trends match observed galaxy data.

Abstract

The abundance evolution of galaxies depends critically on the balance between the mixing of metals in their interstellar medium, the inflow of new gas and the outflow of enriched gas. We study these processes in gas columns perpendicular to a galactic disk using sub-parsec resolution simulations that track stellar ejecta with the Flash code. We model a simplified interstellar medium stirred and enriched by supernovae and their progenitors. We vary the density distribution of the gas column and integrate our results over an exponential disk to predict wind and ISM enrichment properties for disk galaxies. We find that winds from more massive galaxies are hotter and more highly enriched, in stark contrast to that which is often assumed in galaxy formation models. We use these findings in a simple model of galactic enrichment evolution, in which the metallicity of forming galaxies is the result of accretion of nearly pristine gas and outflow of enriched gas along an equilibrium sequence. We compare these predictions to the observed mass-metallicity relation, and demonstrate how the galaxy's gas fraction is a key controlling parameter. This explains the observed flattening of the mass-metallicity relation at higher stellar masses.