The Gas Mass Reservoir of Quiescent Galaxies at Cosmic Noon

We present a 1.1mm stacking analysis of moderately massive (log(\(M_{*}\)/\(M_{\odot}\)) = 10.7 \(\pm\) 0.2) quiescent galaxies (QGs) at \(\langle z\rangle \sim1.5\), searching for cold dust continuum emission, 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 dust continuum equivalent of dust mass log(\(M_{dust}\)/\(M_{\odot}\)) = 7.47 \(\pm\) 0.13 and gas mass log(\(M_{gas}\)/\(M_{\odot}\)) = 9.42 \(\pm\) 0.14. The emerging gas fraction is \(f_{gas}\) = 5.3 \(\pm\) 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 have an order of magnitude larger \(f_{gas}\) compared to their local counterparts and have experienced quenching with a non negligible gas reservoir in their interstellar medium - i.e. with gas retention. 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 haloes. 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 the studies of individual targets that favour a fully depleted ISM in massive (log(\(M_{*}\)/\(M_{\odot}\)) high-z QGs.