A mature galaxy cluster at z=1.58 around the radio galaxy 7C1753+6311
  We report on the discovery of a z=1.58 mature cluster around the
high-redshift radio galaxy 7C1753+6311, first identified in the Clusters Around
Radio-Loud AGN survey. Two-thirds of the excess galaxies within the central
1Mpc lie on a red sequence with a colour that is consistent with an average
formation redshift of zf~3. We show that 80+/-6% of the red sequence galaxies
in the cluster core are quiescent, while the remaining 20% are red due to dusty
star formation. We demonstrate that the cluster has an enhanced quiescent
galaxy fraction that is three times that of the control field. We also show
that this enhancement is mass dependent: 91+/-9% of the M* >10^{10.5}Msun
cluster galaxies are quiescent, compared to only 36+/-2% of field galaxies,
whereas the fraction of quiescent galaxies with lower masses is the same in the
cluster and field environments. The presence of a dense core and a well-formed,
quiescent red sequence suggest that this is a mature cluster. This means that
distant radio galaxies do not solely reside in young, uncollapsed
protoclusters, rather they can be found in clusters in a wide range of
evolutionary states.
