What determines the HI gas content in galaxies?: morphological dependence of the HI gas fraction across M*-SFR plane

Abstract

We perform a stacking analysis of the H I spectra from the Arecibo Legacy Fast ALFA (ALFALFA) survey for optically-selected local galaxies from the Sloan Digital Sky Survey (SDSS) to study the average gas fraction of galaxies at fixed stellar mass (M * ) and star formation rate (SFR). We first confirm that the average gas fraction strongly depends on the stellar mass and SFR of host galaxies; massive galaxies tend to have a lower gas fraction, and actively star-forming galaxies show higher gas fraction, which is consistent with many previous studies. Then we investigate the morphological dependence of the H I gas mass fraction at fixed M * and SFR to minimize the effects of these parameters. We use three morphological classifications based on parametric indicator (Sérsic index), non-parametric indicator (C-index), and visual inspection (smoothness from the Galaxy Zoo 2 project) on the optical image. We find that there is no significant morphological dependence of the H I gas mass fraction at fixed M * and SFR when we use C-index. In comparison, there exists a hint of diminishment in the H I gas mass fraction for "smooth" galaxies compared with "non-smooth" galaxies. We find that the visual smoothness is sensitive to the existence of small-scale structures in a galaxy. Our result suggests that even at fixed M * and SFR, the presence of such small-scale structures (seen in the optical image) is linked to their total H I gas content.

A new technique to isolate kinematically anomalous gas in H i data cubes

“…Moura et al (2020) infer the loss of ionized gas in galaxies located in compact groups due to their environment, although the effect is small. However, a more recent study in Namiki et al (2021) finds that H i scaling relations are not driven by the environmental density per se.…”