http://arxiv.org/abs/1808.10501
The neutral hydrogen (HI) gas is an important barometer of recent star formation and metal enrichment activities in galaxies. We develop a novel statistical method for predicting the HI-to-stellar mass ratio $f_{\mathrm{gas}}$ of galaxies from their stellar mass and optical colour, and apply it to a volume-limited galaxy sample jointly observed by the Sloan Digital Sky Survey and the Arecibo Legacy Fast ALFA survey. We eliminate the impact of the Malmquist bias against HI-deficient systems on the $f_{\mathrm{gas}}$ predictor by properly accounting for the HI detection probability of each galaxies in the analysis. The best-fitting $f_{\mathrm{gas}}$ predictor, with an estimated scatter of $0.272$ dex, provides excellent description to the observed HI mass function. After defining an HI excess parameter as the deviation of the observed $f_{\mathrm{gas}}$ from the expected value, we confirm that there exists a strong secondary dependence of the mass-metallicity relation on HI excess. By further examining the 2D metallicity distribution on the specific star formation rate vs. HI excess plane, we demonstrate that the metallicity dependence on HI is more fundamental than that on specific star formation rate. In addition, we show that the environmental dependence of HI in the local Universe can be effectively described by the cross-correlation coefficient between HI excess and the red galaxy overdensity $\rho_{cc}{=}-0.18$. This weak anti-correlation also successfully explains the observed dependence of HI clustering on $f_{\mathrm{gas}}$. Our method provides a useful framework for learning HI gas evolution from the synergy between future HI and optical galaxy surveys.
Y. Zu
Mon, 3 Sep 18
24/54
Comments: 14 pages, 9 figures, comments welcome