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

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.