Evolution of the X-ray Profiles of Poor Clusters from the XMM-LSS Survey

TL;DR

This study analyzes the evolution of X-ray surface brightness profiles in 27 poor galaxy clusters from the XMM-LSS survey, revealing that cuspy cool cores are more prominent at higher redshifts and that the outer slope correlates with redshift and temperature.

Contribution

It provides new insights into the evolution of cool cores and surface brightness profiles in poor clusters across a wide redshift range, challenging previous findings for rich clusters.

Findings

Cuspy cool cores are more prominent at higher redshifts.

The outer slope beta correlates positively with redshift and temperature.

Incidence of cool cores does not decline at high redshift.

Abstract

A sample consisting of 27 X-ray selected galaxy clusters from the XMM-LSS survey is used to study the evolution in the X-ray surface brightness profiles of the hot intracluster plasma. These systems are mostly groups and poor clusters, with temperatures 0.6-4.8 keV, spanning the redshift range 0.05 to 1.05. Comparing the profiles with a standard beta-model motivated by studies of low redshift groups, we find 54% of our systems to possess a central excess, which we identify with a cuspy cool core. Fitting beta-model profiles, allowing for blurring by the XMM point spread function, we investigate trends with both temperature and redshift in the outer slope (beta) of the X-ray surface brightness, and in the incidence of cuspy cores. Fits to individual cluster profiles and to profiles stacked in bands of redshift and temperature indicate that the incidence of cuspy cores does not decline at high redshifts, as has been reported in rich clusters. Rather such cores become more prominent with increasing redshift. Beta shows a positive correlation with both redshift and temperature. Given the beta-T trend seen in local systems, we assume that temperature is the primary driver for this trend. Our results then demonstrate that this correlation is still present at z~0.3, where most of our clusters reside.