Massive quenched galaxies at z~0.7 retain large molecular gas reservoirs

TL;DR

This study reveals that massive post-starburst galaxies at z~0.7 retain large molecular gas reservoirs, challenging models that assume quenching involves complete gas depletion.

Contribution

First direct measurements of molecular gas in massive post-starburst galaxies at intermediate redshift, showing they retain substantial gas despite quenching.

Findings

Massive post-starburst galaxies at z~0.7 have large molecular gas reservoirs.

These galaxies' gas content is an order of magnitude higher than local counterparts.

Quenching may occur without complete removal of molecular gas.

Abstract

The physical mechanisms that quench star formation, turning blue star-forming galaxies into red quiescent galaxies, remain unclear. In this Letter, we investigate the role of gas supply in suppressing star formation by studying the molecular gas content of post-starburst galaxies. Leveraging the wide area of the SDSS, we identify a sample of massive intermediate-redshift galaxies that have just ended their primary epoch of star formation. We present ALMA CO(2-1) observations of two of these post-starburst galaxies at z~0.7 with M* ~ 2x10^11 Msun. Their molecular gas reservoirs of (6.4 +/- 0.8) x 10^9 Msun and (34.0 +/- 1.6) x 10^9 Msun are an order of magnitude larger than comparable-mass galaxies in the local universe. Our observations suggest that quenching does not require the total removal or depletion of molecular gas, as many quenching models suggest. However, further observations are required both to determine if these apparently quiescent objects host highly obscured star formation and to investigate the intrinsic variation in the molecular gas properties of post-starburst galaxies.