Solar chemical composition in the hot gas of cool-core ellipticals, groups, and clusters of galaxies

TL;DR

This study revisits the chemical composition of the hot gas in galaxy clusters and ellipticals, finding consistent solar abundance ratios across different systems and aligning with recent Hitomi observations.

Contribution

It updates previous spectral analyses using an improved code, confirming solar abundance ratios in the ICM and resolving previous discrepancies.

Findings

Cr/Fe and Ni/Fe ratios are close to unity.

Results are consistent with Hitomi measurements.

Solar composition is common in cool-core systems.

Abstract

The hot intracluster medium (ICM) pervading galaxy clusters and groups is rich in metals, which were synthesised by billions of supernovae and have accumulated in cluster gravitational wells for several Gyrs. Since the products of both Type Ia and core-collapse supernovae - expected to explode over different time scales - are found in the ICM, constraining accurately the chemical composition these hot atmospheres can provide invaluable information on the history of the enrichment of large-scale structures. Recently, Hitomi observations reported solar abundance ratios in the core of the Perseus cluster, in tension with previous XMM-Newton measurements obtained for 44 cool-core clusters, groups, and massive ellipticals (the CHEERS sample). In this work, we revisit the CHEERS results by using an updated version of the spectral code used to fit the data (SPEXACT v3), the same as was used to obtain the Hitomi measurements. Despite limitations in the spectral resolution, the average Cr/Fe and Ni/Fe ratios are now found to be remarkably consistent with unity and in excellent agreement with the Hitomi results. Our updated measurements suggest that the solar composition of the ICM of Perseus is a very common feature in nearby cool-core systems.