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