The XXL Survey: XXX. Characterisation of the XLSSsC N01 supercluster and
  analysis of the galaxy stellar populations
  Superclusters form from the largest enhancements in the primordial density
perturbation field and extend for tens of Mpc, tracing the large-scale
structure of the Universe. We characterise XLSSsCN01, a rich supercluster at
z~0.3 detected in the XXL Survey, composed of X-ray clusters of different
virial masses and luminosities. As one of the first studies on this topic, we
investigate the stellar populations of galaxies in different environments in
the supercluster region. We study a magnitude-limited (r<=20) and a
mass-limited sample (log(M*/M_sun)>10.8) of galaxies in the virialised region
and in the outskirts of 11 XLSSsCN01 clusters, in high- and low-density field.
We compute the stellar population properties of galaxies using spectral energy
distribution and spectral fitting techniques, and study the dependence of star
formation rates (SFR), colours, and stellar ages on environment. For r<20, the
fraction of SFing/blue galaxies, computed either from the specific-SFR (sSFR)
or rest-frame(rf) colour, shows depletion within the cluster virial radii,
where the number of galaxies with log(sSFR/yr^-1)>-12 and with (g-r)_rf<0.6 is
lower than in the field. For log(M*/M_sun)>10.8, no trends with environment
emerge, as massive galaxies are mostly already passive in all environments. No
differences among low- and high-density field members and cluster members
emerge in the sSFR-mass relation. The luminosity-weighted age-mass relation of
the passive populations within cluster virial radii show signatures of recent
environmental quenching. The study of luminous and massive galaxies in this
supercluster shows that while environment has a prominent role in determining
the fractions of SFing/blue galaxies, its effects on the star formation
activity in SFing galaxies are negligible.
