Evolution of the Intracluster Medium Between 0.2 < z < 1.3 in a Chandra Sample of 70 Galaxy Clusters

Abstract

We study the evolution of the ICM with a sample of 70 galaxy clusters spanning 0.18 < z < 1.24. We find that X-ray luminosity and ICM mass at a fixed temperature evolve with redshift in a manner inconsistent with the standard self-similar model of cluster formation. Both luminosity and ICM mass evolve more slowly toward high redshift than the self-similar prediction. We find that evolution in these two observables can be modeled by a simple evolution in the cluster gas mass fraction. Excluding cluster cores from measurements results in evolution more consistent with the self-similar model than when the entire cluster is used, indicating that the fraction of clusters with cool cores increases with time, or that cool cores become more developed over time in those clusters that have them; this is supported by direct study of the redshift dependence of central surface brightness, which increases in scatter and magnitude at low redshift. We find that isophotal size-temperature relations evolve differently according to which isophote is used, indicating that the central and outer regions of cluster ICM evolve differently. We show that constraints on the evolution of the gas fraction and isophotal size-temperature relations constraints can be combined to measure cluster distances, and thus to constrain cosmological parameters. There are indications that scaling relation scatter decreases at higher redshift, suggesting that merging is not the dominant source of cluster structural variation. Our results provide constraints for simulations attempting to model cluster physics, indicate some difficulties for cosmological studies that assume constant cluster gas fractions, and point toward other potentially more robust uses of clusters for cosmological applications. (Abridged)