The strong correlation between post-starburst fraction and environment

We examine a magnitude limited (MB <-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 - 1.5Gyr), 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 10^11Msun haloes to ~15% in the most massive haloes (10^15.5Msun). Our analysis does not allow us to definitely identify the main mechanisms responsible for the appearance of the PSB spectrum. However, the higher incidence of PSB galaxies in the densest environments suggests that the processes operating in the most massive haloes, such as ram pressure stripping, are more effective in producing such population than the processes operating in the sparsest environments, most likely galaxy interactions.