Metal Production in Galaxy Clusters: The Non-Galactic Component

TL;DR

This paper investigates the origin of metallicity in galaxy clusters and finds that most heavy elements are likely produced outside of galaxies, challenging the traditional view that stars within galaxies are the primary source.

Contribution

It demonstrates that cluster metallicity correlates with total baryonic mass rather than galaxy stellar mass, suggesting a non-galactic origin of metals.

Findings

Metallicity decreases with star-to-baryon ratio.

Metallicity is independent of galaxy mass within clusters.

Most heavy elements are produced outside galaxies.

Abstract

The metallicity in galaxy clusters is expected to originate from the stars in galaxies, with a population dominated by high mass stars likely being the most important stellar component, especially in rich clusters. We examine the relationship between the metallicity and the prominence of galaxies as measured by the star to baryon ratio, M$_*$/M$_{bary}$. Counter to expectations, we rule out a metallicity that is proportional to M$_*$/M$_{bary}$, where the best fit has the gas phase metallicity decreasing with M$_*$/M$_{bary}$, or the metallicity of the gas plus the stars being independent of M$_*$/M$_{bary}$. This implies that the population of stars responsible for the metals is largely proportional to the total baryonic mass of the cluster, not to the galaxy mass within the cluster. If generally applicable, most of the heavy elements in the universe were not produced within galaxies.