Evidence of a link between the evolution of clusters and their AGN fraction

Abstract

We discuss the optical properties, X-ray detections, and Active Galactic Nucleus (AGN) populations of four clusters at z ~ 1 in the Subaru-XMM Deep Field (SXDF). The velocity distribution and plausible extended X-ray detections are examined, as well as the number of X-ray point sources and radio sources associated with the clusters. We find that the two clusters that appear virialised and have an extended X-ray detection contain few, if any, AGN, whereas the two pre-virialised clusters have a large AGN population. This constitutes evidence that the AGN fraction in clusters is linked to the clusters' evolutionary stage. The number of X-ray AGN in the pre-virialised clusters is consistent with an overdensity of factor ~ 200; the radio AGN appear to be clustered with a factor of three to six higher. The median K-band luminosities of L_K = 1.7 +/- 0.7 L* for the X-ray sources and L_K = 2.3 +/- 0.1 L* for the radio sources support the theory that these AGN are triggered by galaxy interaction and merging events in sub-groups with low internal velocity distributions, which make up the cluster environment in a pre-virialisation evolutionary stage.

19 pages, 19 figures, accepted for publication in MNRAS. Note that the figures in this version are of low resolution. A high-resolution version can be downloaded from http://www.carolinevanbreukelen.com/cvb_agn_in_clustersv3.pdf

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• Multiwavelength characterization of faint Ultra Steep Spectrum radio sources : A search for high-redshift radio galaxies
• The Obscured Fraction of Quasars at Cosmic Noon
• More connected, more active: galaxy clusters and groups at z~1 and the connection between their quiescent galaxy fractions and large-scale environments
• On the nature of infrared-faint radio sources in the SXDF and VLA-VVDS fields