CARLA J1753+6311: A mature structure around a z=1.58 radio-loud AGN

In the last few years the number of high redshift protoclusters has rapidly increased by utilizing radio-loud AGN (RLAGN) as beacons for overdense regions at z>1.3. However, there has been some debate over whether these structures are representative of protoclusters as a whole or whether they preferentially select young structures. I will present our recent discovery of a z=1.58 mature cluster from the Clusters Around Radio-Loud AGN survey. Over half of the cluster galaxies lie on a red sequence with a colour that suggests an average formation redshift of z=3. I will show that 82% of the red galaxies in the core are passive and demonstrate that the cluster has an enhanced passive galaxy fraction that is three times that of the control field. Interestingly, this enhancement is mass dependent: the higher passive fraction is only observable for high mass galaxies, whereas the fraction of passive galaxies at lower masses is similar in the cluster and field. The presence of a dense core and a passive red sequence suggest that radio galaxies do not solely reside in young, uncollapsed protoclusters, rather they can be used as beacons for clusters in a wide range of evolutionary states