A Mature Galaxy Cluster at z = 1.58 around the Radio Galaxy 7C 1753+6311
We report on the discovery of a z = 1.58 mature cluster around the high-redshift radio galaxy 7C 1753+6311, first identified in the Clusters Around Radio-loud active galactic nuclei survey. Two-thirds of the excess galaxies within the central 1 Mpc lie on a red sequence with a color that is consistent with an average formation redshift of z_f ~ 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) M_⊙ 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.
Additional Information© 2016. The American Astronomical Society. Received 2015 September 21; accepted 2015 November 10; published 2016 January 14. The authors would like to thank Omar Almaini for making the UDS catalogs and images available and the staff at the WHT for taking the service mode observations. We thank the anonymous referee for their careful review of the manuscript and their helpful comments which improved the content of the paper. E.A.C. acknowledges the support of the STFC. N.A.H. is supported by an STFC Rutherford Fellowship. The work of D.S. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work was based on observations made with the William Herschel Telescope under programme IDs W/2013b/10 and SW2015a07 and with the Spitzer Space Telescope. The William Herschel Telescope and its service programme are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are very grateful to have the opportunity to conduct observations from this mountain.
Published - Cooke_2016p83.pdf