Letter to the Editor

The AGN fraction–velocity dispersion relation in clusters of galaxies

¹ European Southern Observatory, Karl Scharzschild Strasse 2, 85748 Garching, Germay e-mail: ppopesso@eso.org
² INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy

Received: 18 August 2006
Accepted: 16 October 2006

Abstract

Context.Some previous investigations have found that the fraction (f_AGN) 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 () 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 f_AGN and 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 f_AGN and for the clusters in two samples, extracted from the catalogs of Popesso et al. (2006a, A&A, in press) and Miller et al. (2005, AJ, 130, 968), and excluding clusters with significant evidence for substructures.

Results.We find a significant anti-correlation. Clusters with lower and, respectively, higher than 500 km s^-1 have AGN fractions of and , on average. The relation can be described by a model that assumes f_AGN is proportional to the galaxies merging rate, plus a constant.

Conclusions.Since f_AGN increases with decreasing , AGNs are likely to have played a significant rôle in heating the intra-cluster medium and driving galaxy evolution in cluster precursors and groups.