Tracing Early Cosmic Chemical Enrichment: A Uniform XMM-Newton Survey of Metallicity in Galaxy Groups and Clusters

TL;DR

This study uses a uniform XMM-Newton survey of galaxy groups and clusters to analyze metallicity profiles, revealing that present stellar populations cannot fully explain observed ICM metallicities, indicating an early enrichment component.

Contribution

It introduces a comprehensive analysis of ICM metallicity using spectral fitting and chemical evolution models, highlighting the need for an early enrichment population beyond current stellar contributions.

Findings

Present-day stars underpredict ICM metallicity.

Evidence for an early enrichment population (EEP).

Radial metallicity gradients in some systems.

Abstract

Observed metal abundances in the intracluster medium (ICM) of galaxy groups and clusters, $Z_{ICM}$, exceed what is expected from present-day stellar populations alone. Galaxy clusters are presumed to be near closed-box systems, allowing constraints to be placed on the origins of metals and stellar populations responsible for $Z_{ICM}$. We present a uniform XMM-Newton survey of 26 galaxy groups and clusters, measuring radial metallicity profiles and relating $Z_{ICM}$ with the stellar fraction $M_*/M_{gas}$. We determine $Z_{ICM}$ via spectral fitting across multiple annuli finding a best fit of $Z_{ICM} = -0.08^{+0.07}_{-0.07}\, log\left(\frac{M_*}{M_{gas}}\right) + 0.30^{+0.06}_{-0.06}$ with intrinsic scatter $\sigma_p = 0.09^{+0.02}_{-0.01}$. We use closed-box chemical evolution models to estimate the metallicity yield from observable stellar populations, incorporating updated supernova yields and corrections for metals locked in remnants, $Z_* = (1.14 \pm 0.52) \, log\left(1 + \frac{M_*}{M_{gas}}\right)$. Our results demonstrate that present-day stellar populations systematically underpredict $Z_{ICM}$, with an inferred excess component increasing in systems with low $M_*/M_{gas}$. This trend supports the need for an early enrichment population (EEP) distinct from visible stars, $Z_{EEP}$. We find this necessity holds when reconsidering the closed-box assumption by removing all galaxy groups, potential leaky systems, deriving $Z_{EEP}$ within $1\sigma$ when including and excluding groups. Three systems (NGC1132, NGC5098, and NGC4325) deviate from the survey trend, exhibiting steep negative radial metallicity gradients and unusually low $Z_{ICM}$. We posit these systems to be late-forming whose ICM enrichment reflects only recent stellar populations. Our analysis quantifies the necessity of an EEP and provides trends for testing cluster chemical evolution models.