The gas mass reservoir of quiescent galaxies at cosmic noon

We present a 1.1 mm stacking analysis of moderately massive (log(M_*/M_⊙) = 10.7 ± 0.2) quiescent galaxies (QGs) at ⟨z⟩∼1.5, searching for cold dust continuum emission, which serves as an excellent tracer of dust and gas mass. Using both the recent GOODS-ALMA survey, as well as the full suite of ALMA Band-6 ancillary data in the GOODS-S field, we report the tentative detection of a dust continuum equivalent of the dust mass log(M_dust/M_⊙) = 7.47 ± 0.13 and gas mass log(M_gas/M_⊙) = 9.42 ± 0.14. The emerging gas fraction is f_gas = 5.3 ± 1.8%, consistent with the results of previous stacking analyses based on lower resolution sub(mm) observations. Our results support the scenario where high-z QGs exhibit a larger f_gas value by one order of magnitude compared to their local counterparts and have experienced quenching with a non-negligible gas reservoir in their interstellar medium, namely, with gas retention. Our subsequent analysis yields an anti-correlation between the f_gas and the stellar mass of QGs, especially in the high-mass end where galaxies reside in the most massive halos. The f_gas − M_* anti-correlation promotes the selection bias as a possible solution to the tension between the stacking results pointing towards gas retention in high-z QGs of moderate M_* and studies of individual targets that favour a fully depleted ISM in massive (log(M_*/M_⊙) > 11.2) high-z QGs.