The AGN fraction – velocity dispersion relation in clusters of galaxies

Context. Some previous investigations have found that the fraction (fAGN ) of active galactic nuclei (AGNs) is lower in clusters than in the field. This can result from the suppression of galaxy-galaxy mergers in high-velocity dispersion (σv) clusters, if the formation and/or fueling of AGNs is directly related to the merging process. Aims. We investigate the existence of a relation between fAGN and σv in galaxy clusters in order to shed light on the formation and evolution processes of AGNs and cluster galaxies. Methods. Using data from the Sloan Digital Sky Survey we determine fAGN and σv for the clusters in two samples, extracted from the catalogs of Popesso et al. (2006a) and Miller et al. (2005), and excluding clusters with significant evidence for substructures. Results. We find a significant fAGN − σv anti-correlation. Clusters with σv lower and, respectively, higher than 500 km s have AGN fractions of 0.21±0.01 and 0.15±0.01, on average. The fAGN −σv relation can be described by a model that assumes fAGN is proportional to the galaxies merging rate, plus a constant. Conclusions. Since fAGN increases with decreasing σv, AGNs are likely to have played a significant rôle in heating the intra-cluster medium and driving galaxy evolution in cluster precursors and groups.