Kavli Affiliate: Jing Wang
| First 5 Authors: Xiao Li, Cheng Li, H. J. Mo, Jianhong Hu, Jing Wang
| Summary:
Using data from ALFALFA, xGASS, HI-MaNGA and SDSS, we identify a sample of 47
"red but HI-rich"(RR) galaxies with $NUV-r > 5$ and unusually high
HI-to-stellar mass ratios. We compare the optical properties and local
environments between the RR galaxies and a control sample of "red and
HI-normal"(RN) galaxies that are matched in stellar mass and color. The two
samples are similar in the optical properties typical of massive red (quenched)
galaxies in the local Universe. The RR sample tends to be associated with
slightly lower density environments and has lower clustering amplitudes and
smaller neighbor counts at scales from several $times$100kpc to a few Mpc. The
results are consistent with that the RR galaxies preferentially locate at the
center of low-mass halos, with a median halo mass $sim 10^{12}h^{-1}M_{odot}$
compared to $sim 10^{12.5}h^{-1}M_{odot}$ for the RN sample. This result is
confirmed by the SDSS group catalog which reveals a central fraction of 89% for
the RR sample, compared to $sim 60%$ for the RN sample. If assumed to follow
the HI size-mass relation of normal galaxies, the RR galaxies have an average
HI-to-optical radius ratio of $R_{HI}/R_{90}sim 4$, four times the average
ratio for the RN sample. We compare our RR sample with similar samples in
previous studies, and quantify the population of RR galaxies using the SDSS
complete sample. We conclude that the RR galaxies form a unique but rare
population, accounting for only a small fraction of the massive quiescent
galaxy population. We discuss the formation scenarios of the RR galaxies.
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