We present ALMA CO ( 2–1 ) detections in 11 gas-rich cluster galaxies at z \sim 1.6 , constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date .
The observations span three galaxy clusters , derived from the Spitzer Adaptation of the Red-sequence Cluster Survey .
We augment the > 5 \sigma detections of the CO ( 2–1 ) fluxes with multi-band photometry , yielding stellar masses and infrared-derived star formation rates , to place some of the first constraints on molecular gas properties in z \sim 1.6 cluster environments .
We measure sizable gas reservoirs of 0.5 - 2 \times 10 ^ { 11 } { M _ { \sun } } in these objects , with high gas fractions ( f _ { gas } ) and long depletion timescales ( \tau ) , averaging 62 % and 1.4 Gyr , respectively .
We compare our cluster galaxies to the scaling relations of the coeval field , in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence .
We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions , at a level of \sim 4 \sigma , but have consistent depletion timescales .
Exploiting CO detections in lower-redshift clusters from the literature , we investigate the evolution of the gas fraction in cluster galaxies , finding it to mimic the strong rise with redshift in the field .
We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters , deeming them as crucial laboratories for future statistical studies .