ALMA pin-points a strong over-density of U/LIRGs in the massive cluster
  XCS J2215 at z=1.46
  We have surveyed the core regions of the z = 1.46 cluster XCS J2215.9-1738
with the Atacama Large Millimeter Array (ALMA) and the MUSE-GALACSI
spectrograph on the VLT. We obtained high spatial resolution observations with
ALMA of the 1.2 mm dust continuum and molecular gas emission in the central
regions of the cluster. These observations detect 14 significant millimetre
sources in a region with a projected diameter of just ~500kpc (~1'). For six of
these galaxies we also obtain 12 CO(2-1) and 12 CO(5-4) line detections,
confirming them as cluster members, and a further five of our millimetre
galaxies have archival 12CO(2-1) detections which also place them in the
cluster. An additional two millimetre galaxies have photometric redshifts
consistent with cluster membership, although neither show strong line emission
in the MUSE spectra. This suggests that the bulk (> 11/14, ~80%) of the
submillimetre sources in the field are in fact luminous infrared galaxies lying
within this young cluster. We then use our sensitive new observations to
constrain the dust-obscured star formation activity and cold molecular gas
within this cluster. We find hints that the cooler dust and gas components
within these galaxies may have been influenced by their environment reducing
the gas reservoir available for their subsequent star formation. We also find
that these actively star- forming galaxies have the dynamical masses and
stellar population ages expected for the progenitors of massive, early-type
galaxies in local clusters potentially linking these populations.
