The XXL Survey: XXXVII. The role of the environment in shaping the
  stellar population properties of galaxies at 0.1<z<0.5
  Exploiting a sample of galaxies drawn from the XXL-N multiwavelength survey,
we present an analysis of the stellar population properties of galaxies at
0.1<z<0.5, by studying galaxy fractions and the star formation rate
(SFR)-stellar mass(M) relation. Furthermore, we exploit and compare two
parametrisations of environment. When adopting a definition of "global"
environment, we consider separately cluster virial/outer members and field
galaxies. When considering the "local" environment, we take into account the
projected number density of galaxies in a fixed aperture of 1Mpc in the sky. We
find that regardless of the environmental definition adopted, the fraction of
blue/star-forming galaxies is the highest in the field/least dense regions and
the lowest in the virial regions of clusters/highest densities. Furthermore,
the fraction of star-forming galaxies is higher than the fraction of blue
galaxies, regardless of the environment. This result is particularly evident in
the virial cluster regions, most likely reflecting the different star formation
histories of galaxies in different environments. Also the overall SFR-M
relation does not seem to depend on the parametrisation adopted. Nonetheless,
the two definitions of environment lead to different results as far as the
fraction of galaxies in transition between the star-forming main sequence and
the quenched regime is concerned. In fact, using the local environment the
fraction of galaxies below the main sequence is similar at low and high
densities, whereas in clusters (and especially within the virial radii) a
population with reduced SFR with respect to the field is observed. Our results
show that the two parametrisations adopted to describe the environment have
different physical meanings, i.e.are intrinsically related to different
physical processes acting on galaxy populations and are able to probe different
physical scales.
