XMM-Newton study of six massive, X-ray luminous galaxy clusters systems in the redshift range z = 0.25 to 0.5

TL;DR

This study uses XMM-Newton data to analyze six massive galaxy clusters at redshifts 0.25-0.5, characterizing their structures, masses, and properties, and discovering additional clusters and a variable AGN in the fields.

Contribution

First detailed X-ray analysis of six previously unobserved massive clusters in this redshift range, including mass estimation and structural characterization.

Findings

Five clusters confirmed as massive; one overestimated due to projection effects.

Discovery of a double cluster system and a dynamically young cluster with substructures.

Identification of a variable X-ray source likely an AGN in the field.

Abstract

Massive galaxy clusters are interesting astrophysical and cosmological study objects, but are relatively rare. In the redshift range z = 0.25 to 0.5 which is, for example, a favourable region for gravitational lensing studies, about 100 such systems are known. Most of them have been studied in X-rays. In this paper we study the six remaining massive clusters in this redshift interval in the highly complete CLASSIX survey which have so far not been observed with sufficiently deep exposures in X-rays. With data from our new XMM-Newton observations we characterise their structures, derive X-ray properties such as the X-ray luminosity and intra-cluster medium temperature and estimate their gas and total masses. We find that one cluster, RXCJ1230.7+3439, is dynamically young with three distinct substructures in the cluster outskirts and RXCJ1310.9+2157/RXCJ1310.4+2151 is a double cluster system. Mass determination is difficult in the systems with substructure. We therefore discuss several methods of mass estimation including scaling relations. In summary we find that five of the six study targets are indeed massive clusters as expected, while the last cluster RXCJ2116.2-0309 is a close projection of a distant and a nearby cluster which has led to a previous overestimation of its mass. In the XMM-Newton observation fields we also find three low redshift clusters close to the targets which are also analysed and described here. In the field of RXCJ2116.2-0309 we discover serendipitously a highly variable X-ray source which has decreased its flux within a year by more than a factor of eight. This source is most probably an AGN.