Nearly all Massive Quiescent Disk Galaxies Have a Surprisingly Large Atomic Gas Reservoir

The massive galaxy population above the characteristic Schechter mass M _∗ ≈ 10^10.6 contributes to about half of the total stellar mass in the local universe. These massive galaxies usually reside in hot dark matter halos above the critical shock-heating mass ∼10¹², where the external cold gas supply to these galaxies is expected to be suppressed. When galaxies run out of their cold gas reservoir, they become dead and quiescent. Therefore, massive quiescent galaxies living in hot halos are commonly believed to be gas-poor. Based on the data from SDSS, ALFALFA, GASS, and COLD GASS surveys, here we show that the vast majority of the massive, quiescent, central disk galaxies in the nearby universe have a remarkably large amount of cold atomic hydrogen gas, surprisingly similar to star-forming galaxies. Both star-forming and quiescent disk galaxies show identical symmetric double-horn H i spectra, indicating similar regularly rotating H i disks. Relative to their star-forming counterparts, massive quiescent central disk galaxies are quenched because of their significantly reduced molecular gas content, lower dust content, and lower star formation efficiency. Our findings reveal a new picture, which clearly demonstrates the detailed star formation quenching process in massive galaxies and provides a stringent constraint on the physical mechanism of quenching.