The Enrichment of the Intracluster Medium

TL;DR

This study quantifies the contributions of intracluster and galactic stars to the iron enrichment of the intracluster medium in galaxy clusters, highlighting the significant role of intracluster stars and the importance of metal loss from galaxies.

Contribution

It provides the first detailed analysis of the relative contributions of BCG, intracluster, and other galactic stars to ICM enrichment using X-ray and optical data.

Findings

Intracluster stars contribute approximately 22-31% of ICM Fe.

Intracluster stars are significant but not sole sources of ICM Fe.

A large galactic metal loss fraction (~84%) is required to explain observed Fe levels.

Abstract

To determine the relative contributions of galactic and intracluster stars to the enrichment of the intracluster medium (ICM), we present X-ray surface brightness, temperature, and Fe abundance profiles for a set of twelve galaxy clusters for which we have extensive optical photometry. Assuming a standard IMF and simple chemical evolution model scaled to match the present-day cluster early-type SN Ia rate, the stars in the brightest cluster galaxy (BCG) plus the intracluster stars (ICS) generate 31^{+11}_{-9}%, on average, of the observed ICM Fe within r_{500} (~ 0.6 times r_{200}, the virial radius). An alternate, two-component SN Ia model (including both prompt and delayed detonations) produces a similar BCG+ICS contribution of 22^{+9}_{-9}%. Because the ICS typically contribute 80% of the BCG+ICS Fe, we conclude that the ICS are significant, yet often neglected, contributors to the ICM Fe within r_{500}. However, the BCG+ICS fall short of producing all the Fe, so metal loss from stars in other cluster galaxies must also contribute. By combining the enrichment from intracluster and galactic stars, we can account for all the observed Fe. These models require a galactic metal loss fraction (0.84^{+0.11}_{-0.14}) that, while large, is consistent with the metal mass not retained by galactic stars. The SN Ia rates, especially as a function of galaxy environment and redshift, remain a significant source of uncertainty in further constraining the metal loss fraction. For example, increasing the SN Ia rate by a factor of 1.8 -- to just within the 2 sigma uncertainty for present-day cluster early-type galaxies -- allows the combined BCG + ICS + cluster galaxy model to generate all the ICM Fe with a much lower galactic metal loss fraction (~ 0.35).