Enhancement of AGN in a protocluster at z=1.6

Abstract

We investigate the prevalence of AGN in the high-redshift protocluster $\mathrm{Cl}0218.3$-$0510$ at $z=1.62$. Using imaging from the Chandra X-ray Telescope, we find a large overdensity of AGN in the protocluster; a factor of $23\pm 9$ times the field density of AGN. Only half of this AGN overdensity is due to the overdensity of massive galaxies in the protocluster (a factor of $11\pm 2$), as we find that $17_{-5}^{+6}\%$ of massive galaxies ($M_{\ast }>10^{10}{\mathrm{M}}_{\odot }$) in the protocluster host an X-ray luminous AGN, compared to $8\pm 1\%$ in the field. This corresponds to an enhancement of AGN activity in massive protocluster galaxies by a factor of $2.1\pm 0.7$ at $1.6\sigma$ significance. We also find that the AGN overdensity is centrally concentrated, located within 3 arcmin and most pronounced within 1 arcmin of the centre of the protocluster. Our results confirm that there is a reversal in the local anti-correlation between galaxy density and AGN activity, so there is an enhancement of AGN in high-redshift protoclusters. We compare the properties of AGN in the protocluster to the field and find no significant differences in the distributions of their stellar mass, X-ray luminosity, or hardness ratio. We therefore suggest that triggering mechanisms are similar in both environments, and that the mechanisms simply occur more frequently in denser environments.

9 pages, 8 figures, Accepted to MNRAS (24th May 2017)

References in corpus (10)

• Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
• The Luminosity Function of X-ray Selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift
• The Structures of Distant Galaxies I: Galaxy Structures and the Merger Rate to z~3 in the Hubble Ultra-Deep Field
• The Evolution of Active Galactic Nuclei in Clusters of Galaxies to Redshift 1.3
• Why z > 1 radio-loud galaxies are commonly located in proto-clusters
• A z=2.5 protocluster associated with the radio galaxy MRC 2104-242: star formation and differing mass functions in dense environments
• The XMM-Newton wide-field survey in the COSMOS field: V. Angular Clustering of the X-ray Point Sources
• Chandra Observations of the Cl1604 Supercluster at z=0.9: Evidence for an Overdensity of Active Galactic Nuclei
• Evidence of a link between the evolution of clusters and their AGN fraction
• The impact of protocluster environments at z = 1.6

Cited by in corpus (1)

• High density of active galactic nuclei in the outskirts of distant galaxy clusters