Cluster and cluster galaxy evolution history from IR to X-ray observations of the young cluster RX J1257.2+4738 at z=0.866

TL;DR

This study reports the discovery and multi-wavelength analysis of a young, massive galaxy cluster at z~0.87, revealing its dynamical state, galaxy population, and unusual X-ray properties, shedding light on cluster evolution at this epoch.

Contribution

It provides the first detailed multi-wavelength characterization of a z~0.87 cluster, highlighting its dynamical youth and atypical X-ray features, advancing understanding of cluster formation.

Findings

The cluster is dynamically young and still collapsing.

It has an unusually high X-ray temperature relative to luminosity.

Approximately 90% of galaxies are detected in the infrared, indicating active star formation.

Abstract

The cosmic time around the z~1 redshift range appears crucial in the cluster and galaxy evolution, since it is probably the epoch of the first mature galaxy clusters. Our knowledge of the properties of the galaxy populations in these clusters is limited because only a handful of z~1 clusters are presently known. In this framework, we report the discovery of a z~0.87 cluster and study its properties at various wavelengths. We gathered X-ray and optical data (imaging and spectroscopy), and near and far infrared data (imaging) in order to confirm the cluster nature of our candidate, to determine its dynamical state, and to give insight on its galaxy population evolution. Our candidate structure appears to be a massive z~0.87 dynamically young cluster with an atypically high X-ray temperature as compared to its X-ray luminosity. It exhibits a significant percentage ~90% of galaxies that are also detected in the 24micron band. The cluster RXJ1257.2+4738 appears to be still in the process of collapsing. Its relatively high temperature is probably the consequence of significant energy input into the intracluster medium besides the regular gravitational infall contribution. A significant part of its galaxies are red objects that are probably dusty with on-going star formation.