Statistics and implications of substructure detected in a representative sample of X-ray clusters

TL;DR

This study analyzes the substructure of 35 X-ray luminous galaxy clusters using X-ray surface brightness measures, revealing correlations with cool cores, BCG ellipticity, and impacts on scaling relations, aiding cosmological understanding.

Contribution

It introduces a comprehensive morphological analysis combining power ratios and centroid shifts to characterize cluster substructure and its relation to other properties.

Findings

Regular clusters are more luminous at fixed temperature.

Disturbed clusters have larger X-ray masses for a given temperature.

Scatter in mass measurements is larger for disturbed clusters.

Abstract

We present a morphological study of 35 X-ray luminous galaxy clusters at 0.15<z<0.3, selected in a similar manner to the Local Cluster Substructure Survey (LoCuSS), for which deep XMM-Newton observations are available. We characterise the structure of the X-ray surface brightness distribution of each cluster by measuring both their power ratios and centroid shift, and thus rank the clusters by the degree of substructure. These complementary probes give a consistent description of the cluster morphologies with some well understood exceptions. We find a remarkably tight correlation of regular morphology with the occurrence of cool cores in clusters. We also compare our measurements of X-ray morphology with measurements of the luminosity gap statistics and ellipticity of the brightest cluster galaxy (BCG). We check how our new X-ray morphological analysis maps onto cluster scaling relations, finding that (i) clusters with relatively undisturbed X-ray morphologies are on average more luminous at fixed X-ray temperature than those with disturbed morphologies, and (ii) disturbed clusters have larger X-ray masses than regular clusters for a given temperature in the M-T relation. We also show that the scatter in the ratio of X-ray and weak lensing based cluster mass measurements is larger for disturbed clusters than for those of more regular morphology. Overall, our results demonstrate the feasibility of assembling a self-consistent picture of the physical structure of clusters from X-ray and optical data, and the potential to apply this in the measurement of cosmological cluster scaling relations.