Large Molecular Gas Reservoirs in Star-forming Cluster Galaxies

We present CO (2−1) observations of 72 galaxies in the nearby, disturbed Antlia Cluster with the Atacama Pathfinder Experiment telescope. The galaxies in our sample are selected to span a wide range of stellar masses (108 M⊙ ≲ M⋆ ≲ 1010 M⊙) and star formation rates (0.0005 M⊙ yr−1 < SFR < 0.3 M⊙ yr−1). Reaching a depth of 23 mJy in 50 km s−1 channels, we report a total CO detection rate of 37.5% and a CO detection rate of 86% for sources within 1 dex of the main sequence. We compare our sample with a similar sample of galaxies in the field, finding that, for a fixed stellar mass and SFR, galaxies in the Antlia Cluster have comparable molecular gas reservoirs to field galaxies. We find that ∼41% (11/27) of our CO detections display non-Gaussian CO (2−1) emission-line profiles, and a number of these sources display evidence of quenching in their optical images. We also find that the majority of our sample lies either just below or far below the main sequence of field galaxies, further hinting at potential ongoing quenching. We conclude that the Antlia Cluster represents an intermediate environment between fields and dense clusters, where the gentler intracluster medium (ICM) allows the cluster members to retain their reservoirs of molecular gas, but in which the disturbed ICM is just beginning to influence the member galaxies, resulting in high SFRs and possible ongoing quenching.