The XXL Survey: XXII. The XXL-North spectrophotometric sample and galaxy
  stellar mass function in X-ray detected groups and clusters
  The fraction of galaxies bound in groups in the nearby Universe is high (50%
at z~0). Systematic studies of galaxy properties in groups are important in
order to improve our understanding of the evolution of galaxies and of the
physical phenomena occurring within this environment. We have built a complete
spectrophotometric sample of galaxies within X-ray detected, optically
spectroscopically confirmed groups and clusters (G&C), covering a wide range of
halo masses at z<= 0.6. In the context of the XXL survey, we analyse a sample
of 164 G&C in the XXL-North region (XXL-N), at z <= 0.6, with a wide range of
virial masses (1.24 x 10^13 <=M_500 M_sun <= 6.63 x 10^14) and X-ray
luminosities ( 2.27 x 10^41 <= L^XXL_500 (erg/s)<= 2.15 x10^44). The G&C are
X-ray selected and spectroscopically confirmed. We describe the membership
assignment and the spectroscopic completeness analysis, and compute stellar
masses. As a first scientific exploitation of the sample, we study the
dependence of the galaxy stellar mass function (GSMF) on global environment. We
present a spectrophotometric characterisation of the G&C and their galaxies.
The final sample contains 132 G&C, 22111 field galaxies and 2225 G&C galaxies
with r-band magnitude <20. Of the G&C, 95% have at least three spectroscopic
members, and 70% at least ten. The shape of the GSMF seems not to depend on
environment (field versus G&C) or X-ray luminosity ( used as a proxy for the
virial mass of the system). These results are confirmed by the study of the
correlation between mean stellar mass of G&C members and L^XXL_500.We release
the spectrophotometric catalogue of galaxies with all the quantities computed
in this work. As a first homogeneous census of galaxies within X-ray
spectroscopically confirmed G&C at these redshifts, this sample will allow
environmental studies of the evolution of galaxy properties.
