Chemical abundances in the outskirts of nearby galaxy groups measured with joint Suzaku and Chandra observations

TL;DR

This study measures chemical abundances in the outskirts of nearby galaxy groups using Suzaku and Chandra data, revealing uniform Fe levels similar to clusters and insights into enrichment history and supernova contributions.

Contribution

First detailed measurement of chemical abundances in galaxy group outskirts, showing uniform Fe levels and comparing them with simulations and cluster data.

Findings

Fe abundance in outskirts is consistent across groups and similar to clusters.

Abundance ratios align with IllustrisTNG predictions, indicating early enrichment.

Iron-mass-to-light ratios are lower than in clusters, suggesting gas loss or different star formation histories.

Abstract

We report results from deep Suzaku and mostly snapshot Chandra observations of four nearby galaxy groups: MKW4, Antlia, RXJ1159+5531, and ESO3060170. Their peak temperatures vary over 2-3 keV, making them the smallest systems with gas properties constrained to their viral radii. The average Fe abundance in the outskirts (R $>$ 0.25R$_{200}$) of their intragroup medium (IGrM) is $Z_{\rm Fe}=0.309\pm0.018$ $Z_\odot$ with $\chi^2$ = 14 for 12 degrees of freedom, which is remarkably uniform and strikingly similar to that of massive galaxy clusters, and is fully consistent with the numerical predictions from the IllustrisTNG cosmological simulation. Our results support an early-enrichment scenario among galactic systems over an order of magnitude in mass, even before their formation. When integrated out to R$_{200}$, we start to see a tension between the measured Fe content in ICM and what is expected from supernovae yields. We further constrain their O, Mg, Si, S, and Ni abundances. The abundance ratios of those elements relative to Fe are consistent with the predictions (if available) from IllustrisTNG. Their Type Ia supernovae fraction varies between 14%-21%. A pure core collapsed supernovae enrichment at group outskirts can be ruled out. Their cumulative iron-mass-to-light ratios within R$_{200}$ are half that of the Perseus cluster, which may imply that galaxy groups do not retain all of their enriched gas due to their shallower gravitational potential wells, or that groups and clusters may have different star formation histories.