Statistics and implications of substructure detected in a representative sample of X-ray clusters
Max-Planck-Institut für extraterrestrische Physik,
2 School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, England
Received: 21 August 2012
Accepted: 16 October 2012
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), to examine recent suggestions that these quantities may be efficient probes of the assembly history of and observer’s viewing angle through cluster-scale mass distributions. Our X-ray analysis confirms that cluster with large luminosity gaps form a relatively homogeneous population that appears more regular with the implication that such systems did not suffer from recent merger activity. Similarly, we find a clear correlation between the ellipticity of the BCGs and the shape of the cluster. In particular nearly circular BCGs (ϵ < 0.2) are found in undisturbed systems with regular X-ray morphologies. For these systems it has been suggested that they are intrinsically prolate and viewed along the line of sight close to the major axis. Finally, 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 MX − 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.
Key words: X-rays: galaxies: clusters / galaxies: clusters: general / cosmology: observations
© ESO, 2012