Gas Density Perturbations in Cool Cores of CLASH Galaxy Clusters

TL;DR

This study investigates gas density perturbations in the cool cores of galaxy clusters, revealing that gas sloshing is common and may help prevent runaway cooling in these environments.

Contribution

It provides a systematic analysis of gas sloshing in relaxed galaxy clusters using X-ray residuals and confirms the phenomenon with hydrodynamic simulations.

Findings

Gas sloshing occurs in over 80% of relaxed clusters.

Positive excess regions have lower ICM temperatures than negative regions.

Gas perturbations are in pressure equilibrium, supporting the sloshing hypothesis.

Abstract

We present a systematic study of gas density perturbations in cool cores of high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool core features observed with the Chandra X-ray Observatory. We focus on the X-ray residual image characteristics after subtracting their global profile of the X-ray surface brightness distribution. We find that all the galaxy clusters in our sample have, at least, both one positive and one negative excess regions in the X-ray residual image, indicating the presence of gas density perturbations. We identify and characterize the locally perturbed regions using our detection algorithm, and extract X-ray spectra of the intracluster medium (ICM). The ICM temperature in the positive excess region is lower than that in the negative excess region, whereas the ICM in both regions is in pressure equilibrium in a systematic manner. These results indicate that gas sloshing in cool cores takes place in more than 80% of relaxed clusters (95% CL). We confirm this physical picture by analyzing synthetic X-ray observations of a cool-core cluster from a hydrodynamic simulation, finding that our detection algorithm can accurately extract both the positive and negative excess regions and can reproduce the temperature difference between them. Our findings support the picture that the gas density perturbations are induced by gas sloshing, and a large fraction of cool-core clusters have undergone gas sloshing, indicating that gas sloshing may be capable of suppressing runaway cooling of the ICM.