Resolving galaxy cluster gas properties at z~1 with XMM-Newton and Chandra

TL;DR

This study combines XMM-Newton and Chandra X-ray data to analyze the gas properties of five massive galaxy clusters at z~1, demonstrating the method's effectiveness for high-redshift cluster analysis.

Contribution

It introduces a new combined XMM-Newton and Chandra approach for spatially-resolved spectroscopy of distant galaxy clusters, enabling detailed thermodynamic analysis.

Findings

No significant deviation from self-similar evolution in scaled profiles.

Baryon mass fraction approaches the cosmic value at high redshift.

Chandra-XMM combination is essential for morphological and substructure analysis.

Abstract

We present a pilot X-ray study of the five most massive ($M_{500}>5 \times 10^{14} M_{\odot}$), distant (z~1), galaxy clusters detected via the Sunyaev-Zeldovich effect. We optimally combine XMM-Newton and Chandra X-ray observations by leveraging the throughput of XMM to obtain spatially-resolved spectroscopy, and the spatial resolution of Chandra to probe the bright inner parts and to detect embedded point sources. Capitalising on the excellent agreement in flux-related measurements, we present a new method to derive the density profiles, constrained in the centre by Chandra and in the outskirts by XMM. We show that the Chandra-XMM combination is fundamental for morphological analysis at these redshifts, the Chandra resolution being required to remove point source contamination, and the XMM sensitivity allowing higher significance detection of faint substructures. The sample is dominated by dynamically disturbed objects. We use the combined Chandra-XMM density profiles and spatially-resolved temperature profiles to investigate thermodynamic quantities including entropy and pressure. From comparison of the scaled profiles with the local REXCESS sample, we find no significant departure from standard self-similar evolution, within the dispersion, at any radius, except for the entropy beyond 0.7$R_{500}$. The baryon mass fraction tends towards the cosmic value, with a weaker dependence on mass than observed in the local Universe. We compare with predictions from numerical simulations. The present pilot study demonstrates the utility and feasibility of spatially-resolved analysis of individual objects at high-redshift through the combination of XMM and Chandra observations. Observations of a larger sample will allow a fuller statistical analysis to be undertaken, in particular of the intrinsic scatter in the structural and scaling properties of the cluster population. (abridged)