Cold gas in the inner regions of intermediate redshift clusters
  Determining gas content and star formation rate has known remarkable progress
in field galaxies, but has been much less investigated in galaxies inside
clusters. We present the first CO observations of luminous infrared galaxies
(LIRGs) inside the virial radii of two intermediate redshift clusters,
CL1416+4446 (z=0.397) and CL0926+1242 (z=0.489). We detect three galaxies at
high significance (5 to 10 sigma), and provide robust estimates of their CO
luminosities, L'CO. In order to put our results into a general context, we
revisit the relation between cold and hot gas and stellar mass in nearby field
and cluster galaxies. We find evidence that at fixed LIR (or fixed stellar
mass), the frequency of high L'CO galaxies is lower in clusters than in the
field, suggesting environmental depletion of the reservoir of cold gas. The
level of star formation activity in a galaxy is primarily linked to the amount
of cold gas, rather than to the galaxy mass or the lookback time. In clusters,
just as in the field, the conversion between gas and stars seems universal. The
relation between LIR and L'CO for distant cluster galaxies extends the relation
of nearby galaxies to higher IR luminosities. Nevertheless, the intermediate
redshift galaxies fall well within the dispersion of the trend defined by local
systems. Considering that L'CO is generally derived from the CO(1-0) line and
sensitive to the vast majority of the molecular gas in the cold interstellar
medium of galaxies, but less to the part which will actually be used to form
stars, we suggest that molecular gas can be stripped before the star formation
rate is affected. Combining the sample of Geach et al. (2009, 2011) and ours,
we find evidence for a decrease in CO towards the cluster centers. This is the
first hint of an environmental impact on cold gas at intermediate redshift.
