The Enrichment of the Intracluster Medium

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 12 galaxy clusters⁴Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. for which we have extensive optical photometry. Assuming a standard initial mass function 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 2σ 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).