Role of environment on nuclear activity
  Motivated by the apparently conflicting results reported in the literature on
the effect of environment on nuclear activity, we have carried out a new
analysis by comparing the fraction of galaxies hosting active galactic nuclei
(AGNs) in the most overdense regions (rich galaxy clusters) and the most
underdense ones (voids) in the local universe. Exploiting the classical BPT
diagnostics, we have extracted volume limited samples of star forming and AGN
galaxies. We find that, at variance with star-forming galaxies, AGN galaxies
have similar distributions of specific star formation rates and of galactic
ages (as indicated by the Dn4000 parameter) both in clusters and in voids. In
both environments galaxies hosting AGNs are generally old, with low star
formation activity. The AGN fraction increases faster with stellar mass in
clusters than in voids, especially above 10^10.2 M(sun). Our results indicate
that, in the local universe, the nuclear activity correlates with stellar mass
and galaxy morphology and is weakly, if at all, affected by the local galaxy
density.
