An X-ray Selected Galaxy Cluster in the Lockman Hole at Redshift 1.753

TL;DR

This paper reports the discovery of a galaxy cluster at redshift 1.753 via X-ray detection, providing insights into early galaxy formation and the properties of brightest cluster galaxies at high redshift.

Contribution

First X-ray selected galaxy cluster at z=1.753 with detailed optical/IR analysis supporting early formation models.

Findings

Cluster's X-ray luminosity measured at 3.68 x 10^43 erg s^-1

Brightest cluster galaxy likely formed around redshift 5

Some candidate members exhibit expected red sequence properties

Abstract

We have discovered an X-ray selected galaxy cluster with a spectroscopic redshift of 1.753. The redshift is of the brightest cluster galaxy (BCG), which is coincident with the peak of the X-ray surface brightness. We also have concordant photometric redshifts for seven additional candidate cluster members. The X-ray luminosity of the cluster is 3.68 +/- 0.70 x 10^43 erg s^-1 in the 0.1 - 2.4 keV band. The optical/IR properties of the BCG imply its formation redshift was ~5 if its stars formed in a short burst. This result continues the trend from lower redshift in which the observed properties of BCGs are most simply explained by a monolithic collapse at very high redshift instead of the theoretically preferred gradual hierarchical assembly at later times. However the models corresponding to different formation redshifts are more clearly separated as our observation epoch approaches the galaxy formation epoch. Although our infrared photometry is not deep enough to define a red sequence, we do identify a few galaxies at the cluster redshift that have the expected red sequence photometric properties.