An X-ray underluminous cluster of galaxies in the 4Ms CDFS observations
  [Abridged] We use the large public spectroscopic database available in the
GOODS-South field to estimate the dynamical mass and the virialization status
of cluster ClG 0332-2747 at z=0.734. Cluster members selected from their
photometric redshift are used with spectroscopic ones to analyse the galaxy
population of the cluster. In the newly released Chandra 4Ms observations we
detect a faint extended X-ray emission associated to the cluster. Finally, we
compare the optical and X-ray properties of ClG 0332-2747 with the predictions
of a well tested semianalytic model. We estimate the velocity dispersion and
the virial mass considering all 44 spectroscopic members, or 20 red-sequence
members only. We obtain sigma_v=634 +/- 105 Km/s, M_200=3.07
^{+1.57}_{-1.16}~10^{14} M_sun in the former case, and slightly lower values in
the latter case. The cluster appears to have reached the virial equilibrium: it
shows a perfectly Gaussian velocity distribution and no evidence for
substructures. ClG 0332-2747 contains a high fraction of bright red galaxies,
and is dominated by a very massive (1.1 x 10^{12} M_sun) old brightest cluster
galaxy (BCG), suggesting that it formed at an early epoch. We detect a faint
extended X-ray source centered on the BCG, with a total X-ray luminosity of L_X
~ 2 x 10^{42} erg s^-1 (0.1-2.4 keV). This L_X is lower by a factor of ~10-20
than expected according to the M-L_X relation. We provide a possible
explanation of this discrepancy as due to the effects of AGN feedback on the
ICM: the semianalytic model reproduces the M-L_X relation measured from "X-ray
bright" clusters, and it predicts a high scatter at low masses due to heating
and expulsion of the cluster gas. Interestingly, in the model clusters with an
evolved galaxy population like ClG 0332-2747 present the largest scatter in
X-ray luminosity.
