The Role of H i in Regulating the Size Growth of Local Galaxies
Abstract We study the role of atomic hydrogen (H i) in regulating the size growth of local galaxies. The size of a galaxy, D r,25, is characterized by the diameter at which the r-band surface brightness reaches μ r = 25.0 mag arcsec − 2 . We find that the positions of galaxies in the size (D r,25)−stellar-mass (M *) plane strongly depend on their H i-to-stellar-mass ratio (M H i /M *). In the H i−rich regime, galaxies that are richer in H i tend to have larger sizes. Such a trend is not seen in the H i–poor regime, suggesting that size growth is barely affected by the H i content when it has decreased to a sufficiently low level. An investigation of the relations between size, M H I/M *, and star formation rate (SFR) suggests that size is more intrinsically linked with M H I/M *, rather than SFR. We further examine the H i-to-stellar-disk size ratio (D H I/D r,25) of galaxies and find that at log(M H I/M *) > −0.7, D H I/D r,25 is weakly correlated with M *. These findings support a picture in which the H i−rich galaxies live in an inside-out disk-growing phase regulated by gas accretion and star formation. The angular momentum of the accreted materials is probably the key parameter in shaping the size of a H i−rich galaxy.