Merger driven star-formation activity in Cl J1449+0856 at z=1.99 as seen
  by ALMA and JVLA
  We use ALMA and JVLA observations of the galaxy cluster Cl J1449+0856 at
z=1.99, in order to study how dust-obscured star-formation, ISM content and AGN
activity are linked to environment and galaxy interactions during the crucial
phase of high-z cluster assembly. We present detections of multiple transitions
of $^{12}$CO, as well as dust continuum emission detections from 11 galaxies in
the core of Cl J1449+0856. We measure the gas excitation properties,
star-formation rates, gas consumption timescales and gas-to-stellar mass ratios
for the galaxies.
  We find evidence for a large fraction of galaxies with highly-excited
molecular gas, contributing $>$50% to the total SFR in the cluster core. We
compare these results with expectations for field galaxies, and conclude that
environmental influences have strongly enhanced the fraction of excited
galaxies in this cluster. We find a dearth of molecular gas in the galaxies'
gas reservoirs, implying a high star-formation efficiency (SFE) in the cluster
core, and find short gas depletion timescales $\tau$<0.1-0.4 Gyrs for all
galaxies. Interestingly, we do not see evidence for increased specific
star-formation rates (sSFRs) in the cluster galaxies, despite their high SFEs
and gas excitations. We find evidence for a large number of mergers in the
cluster core, contributing a large fraction of the core's total star-formation
compared with expectations in the field. We conclude that the environmental
impact on the galaxy excitations is linked to the high rate of galaxy mergers,
interactions and active galactic nuclei in the cluster core.
