A statistically-selected Chandra sample of 20 galaxy clusters -- II. Gas properties and cool-core/non-cool core bimodality

TL;DR

This study analyzes the thermodynamic and chemical properties of 20 galaxy clusters using Chandra data, revealing bimodality in entropy profiles and differences between cool-core and non-cool-core clusters, with implications for thermal stabilization mechanisms.

Contribution

It provides the first detailed statistical comparison of gas properties in cool-core and non-cool-core galaxy clusters, highlighting entropy bimodality and the role of thermal conduction and feedback.

Findings

Entropy profiles show bimodality, with steeper profiles in CC clusters.

Metallicity declines with radius similarly in all clusters.

Thermal conduction alone can stabilize non-CC clusters, but CC clusters require additional feedback.

Abstract

We investigate the thermodynamic and chemical structure of the intracluster medium (ICM) across a statistical sample of 20 galaxy clusters analysed with the Chandra X-ray satellite. In particular, we focus on the scaling properties of the gas density, metallicity and entropy and the comparison between clusters with and without cool cores (CCs). We find marked differences between the two categories except for the gas metallicity, which declines strongly with radius for all clusters (Z ~ r^{-0.31}), outside ~0.02 r500. The scaling of gas entropy is non-self-similar and we find clear evidence of bimodality in the distribution of logarithmic slopes of the entropy profiles. With only one exception, the steeper sloped entropy profiles are found in CC clusters whereas the flatter slope population are all non-CC clusters. We explore the role of thermal conduction in stabilizing the ICM and conclude that this mechanism alone is sufficient to balance cooling in non-CC clusters. However, CC clusters appear to form a distinct population in which heating from feedback is required in addition to conduction. Under the assumption that non-CC clusters are thermally stabilized by conduction alone, we find the distribution of Spitzer conduction suppression factors, f_c, to be log-normal, with a log (base 10) mean of -1.50+/-0.03 (i.e. f_c=0.032) and log standard deviation 0.39+/-0.02.