The strong correlation between post-starburst fraction and environment
  We examine a magnitude limited (M_B< -18.7) sample of post-starburst (PSB)
galaxies at 0.03<z<0.11 in the different environments from the spectroscopic
data set of the Padova Millennium Galaxy Group Catalog and compare their
incidence and properties with those of passive (PAS) and emission line galaxies
(EML). PSB galaxies have a quite precise life-time (<1-1.5 Gyr), and they hold
important clues for understanding galaxy evolution. While the properties
(stellar mass, absolute magnitude, color) of PSBs do not depend on environment,
their frequency increases going from single galaxies to binary systems to
groups, both considering the incidence with respect to the global number of
galaxies and to the number of currently+recently star-forming galaxies.
Including in our analysis the sample of cluster PSBs drawn from the WIde-field
Nearby Galaxy-cluster Survey presented in Paccagnella et al., we extend the
halo mass range covered and present a coherent picture of the effect of the
environment on galaxy transformations. We find that the PSB/(PSB+EML) fraction
steadily increases with halo mass going from 1% in 10^{11} M_sun$ haloes to
~15% in the most massive haloes (10^{15.5} M_sun). This provides evidence that
processes specific to the densest environments, such as ram pressure stripping,
are responsible for a large fraction of PSB galaxies in dense environments.
These processes act on a larger fraction of galaxies than alternative processes
leading to PSB galaxies in the sparsest environments, such as galaxy
interactions.
