The XMM-LSS Survey. First high redshift galaxy clusters: relaxed and collapsing systems

TL;DR

This paper reports the discovery of five high-redshift galaxy clusters from the XMM-LSS survey, analyzing their X-ray properties, redshifts, and dynamical states, revealing less massive but scaling-relation consistent clusters at z>0.6.

Contribution

First identification and characterization of five high-redshift galaxy clusters using XMM-LSS data, including spectroscopic confirmation and analysis of their physical properties.

Findings

Three clusters have measured velocity dispersions and X-ray properties consistent with low-redshift scaling relations.

One cluster is identified via galaxy overdensity matching its redshift, despite limited spectroscopic confirmation.

The highest redshift candidate may be a double cluster complex at z~1.

Abstract

We present five newly found galaxy clusters at z>0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at z=0.613 and \sigma_V=867^{+80}_{-60} km/s, XLSSC 002 at z=0.772 and \sigma_V=524^{+267}_{-116} km/s and XLSSC 003 at z=0.839 and \sigma_V=780^{+137}_{-75} km/s. These three clusters have X-ray bolometric luminosities L_X \sim 1-3 \times 10^{44} erg/s and temperatures 2-4 keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between L_X, T and \sigma_V, within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour R-z'=1.4 that matches the redshift of the central galaxy z=0.87, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure.