Environmental impacts on molecular gas in protocluster galaxies at z~2
  We present the results from ALMA CO(3-2) observations of 66 Halpha-selected
galaxies in three protoclusters around radio galaxies, PKS1138-262 (z=2.16) and
USS1558-003 (z=2.53), and 4C23.56 (z=2.49). The pointing areas have an
overdensity of ~100 compared to a mean surface number density of galaxies in
field environments. We detect CO emission line in 16 star-forming galaxies,
including previously published six galaxies, to measure the molecular gas mass.
In the stellar mass range of 10.5<log(Mstar/Msolar)<11.0, the protocluster
galaxies have larger gas mass fractions and longer gas depletion timescales
compared to the scaling relations established by field galaxies. On the other
hand, the amounts of molecular gas in more massive galaxies with
log(Mstar/Msolar)>11.0 are comparable in mass to the scaling relation, or
smaller. Our results suggest that the environmental effects on gas properties
are mass-dependent: in high-density environments, gas accretion through cosmic
filaments is accelerated in less massive galaxies while this is suppressed in
the most massive system.
