The AGN fraction - velocity dispersion relation in clusters of galaxies
Abstract
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 (sigmav) clusters, if the formation and/or fueling of AGNs is directly related to the merging process. We investigate the existence of a relation between fAGN and sigmav in galaxy clusters in order to shed light on the formation and evolution processes of AGNs and cluster galaxies. Using data from the Sloan Digital Sky Survey we determine fAGN and sigmav 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. We find a significant fAGN-sigmav anti-correlation. Clusters with sigmav 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-sigmav relation can be described by a model that assumes fAGN is proportional to the galaxies merging rate, plus a constant. Since fAGN increases with decreasing sigmav, AGNs are likely to have played a significant role in heating the intra-cluster medium and driving galaxy evolution in cluster precursors and groups.
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