The evolution of mass profiles of galaxy clusters
  We determine the average mass profile of galaxy clusters at two different
redshifts and compare its evolution with cosmological model predictions. We use
two samples of galaxy clusters spanning similar (evolutionary corrected) mass
ranges at different redshifts. The sample of low-redshift (z ~ 0.0-0.1)
clusters is extracted from the ESO Nearby Abell Cluster Survey (ENACS) catalog.
The sample of high-redshift (z ~ 0.4-0.8) clusters is mostly made of clusters
from the ESO Distant Cluster Survey (EDisCS). We determine the average
mass-profiles for these two cluster samples by solving the Jeans equation for
hydrostatic equilibrium, using galaxies as tracers. By using two cluster galaxy
populations, characterized by the presence and, respectively, absence of
emission-lines in their spectra ('ELGs' and 'nELGs' hereafter), we are able to
partially break the mass-profile orbital-anisotropy degeneracy. We find that
the mass-profiles of both the nearby and the distant clusters are reasonably
well fitted by a Navarro, Frenk and White (NFW) model. The best-fit values of
the NFW concentration parameter are as predicted by cosmological numerical
simulations; cluster mass-density profiles become more concentrated with time.
The evolution of the number-density profile of nELGs proceeds in the opposite
sense, becoming less concentrated with time. In our analysis we also recover
the orbital anisotropy of nELGs and ELGs . We find that in low-z clusters nELGs
follow almost isotropic orbits and ELGs have more radially-elongated orbits. In
high-z clusters both nELGs and ELGs follow radially-elongated orbits. We
discuss these results in terms of the predicted secular mass growth of galaxy
clusters and the transformation of ELGs into nELGs.
