Structure and substructure analysis of DAFT/FADA galaxy clusters in the
  [0.4-0.9] redshift range
  We analyse the structures of all the clusters in the DAFT/FADA survey for
which XMM-Newton and/or a sufficient number of galaxy redshifts in the cluster
range is available, with the aim of detecting substructures and evidence for
merging events. These properties are discussed in the framework of standard
cold dark matter cosmology.XMM-Newton data were available for 32 clusters, for
which we derive the X-ray luminosity and a global X-ray temperature for 25 of
them. For 23 clusters we were able to fit the X-ray emissivity with a
beta-model and subtract it to detect substructures in the X-ray gas. A
dynamical analysis based on the SG method was applied to the clusters having at
least 15 spectroscopic galaxy redshifts in the cluster range: 18 X-ray clusters
and 11 clusters with no X-ray data. Only major substructures will be detected.
Ten substructures were detected both in X-rays and by the SG method. Most of
the substructures detected both in X-rays and with the SG method are probably
at their first cluster pericentre approach and are relatively recent infalls.
We also find hints of a decreasing X-ray gas density profile core radius with
redshift. The percentage of mass included in substructures was found to be
roughly constant with redshift with values of 5-15%, in agreement both with the
general CDM framework and with the results of numerical simulations. Galaxies
in substructures show the same general behaviour as regular cluster galaxies;
however, in substructures, there is a deficiency of both late type and old
stellar population galaxies. Late type galaxies with recent bursts of star
formation seem to be missing in the substructures close to the bottom of the
host cluster potential well. However, our sample would need to be increased to
allow a more robust analysis.
