Speaker
Description
Generally, most of the red galaxies in the local universe are observed to be quenched and have little cold gas, suggesting that the depletion/removal of cold gas is a necessary condition for galaxy quenching. However, current HI surveys are too shallow to detect the HI gas of red galaxies. In this work, we construct a new HI estimator based on the scaling relations of HI gas mass with a variety of optical properties of galaxies, and we apply it to the SDSS galaxy sample to study the HI properties of general galaxy populations like HI mass function (HIMF), conditional HIMF (CHIMF), and HI-halo mass relation. Based on the predicted HI masses by our model, we select a sample of red but HI-rich (RR) galaxies and compare their statistical properties with a control sample of red but HI-normal galaxies (RN). We find RR galaxies are similar to RN galaxies in all the optical properties considered once the two samples are closely matched in stellar mass. On average the HI disk size of the RR galaxies as inferred from the HI size-mass relation is larger than the optical size by a factor of ~3, while the HI and optical sizes are comparable for RN galaxies. This result indicates that the large cold gas reservoir of the RR galaxies is due to the substantially low surface density of the extended HI disk, although the formation process of the HI disk still remains unclear.
