The AGN fraction–velocity dispersion relation in clusters of galaxies

Free access article

Issue		A&A Volume 460, Number 2, December III 2006


Page(s)		L23 - L26
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20066269

A&A 460, L23-L26 (2006)
DOI: 10.1051/0004-6361:20066269

Letter

The AGN fraction-velocity dispersion relation in clusters of galaxies

P. Popesso¹ and A. Biviano²

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 ( $f_{\rm AGN}$ ) 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 ( $\sigma_v$ ) 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 $f_{\rm AGN}$ and $\sigma_v$ 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 $f_{\rm AGN}$ and $\sigma_v$ 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 $f_{\rm AGN}{-}\sigma_v$ anti-correlation. Clusters with $\sigma_v$ lower and, respectively, higher than 500 km s^-1 have AGN fractions of $0.21 \pm 0.01$ and $0.15 \pm 0.01$ , on average. The $f_{\rm AGN}{-}\sigma_v$ relation can be described by a model that assumes $f_{\rm AGN}$ is proportional to the galaxies merging rate, plus a constant.
Conclusions.Since $f_{\rm AGN}$ increases with decreasing $\sigma_v$ , AGNs are likely to have played a significant rôle in heating the intra-cluster medium and driving galaxy evolution in cluster precursors and groups.

Key words: galaxies: clusters: general -- galaxies: active -- galaxies: interactions -- Galaxy: kinematics and dynamics

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