FEASTS: Radial Distribution of H i Surface Densities Down to 0.01 M_⊙pc⁻² of 35 Nearby Galaxies

We present the H i surface density (ΣH i) radial distributions based on total-power H i images obtained by FAST in the FEASTS program, for 35 galaxies with inclinations lower than 72°. We derive the H i radius R001, which is the radius for the 0.01 M⊙ pc−2 (~1018.1 cm−2) isodensity level, 100 times deeper than the 1 M⊙ pc−2 level previously commonly used to measure R1. The profile shapes show a large diversity at a given radius in units of kpc, group virial radius, and R1, but they align more tightly with the radius normalized by R001. The universal H i profile has a scatter of ~0.2 dex and a scale length of ~0.11R001 in the outer region. We derive a new R001-MH i relation, which has a scatter of 0.03 dex and a similar slope of ~​​​​​​0.5 to the previously known R1-MH i relation. Excluding strongly tidal-interacting galaxies, the ratio R001/R1 (anti)correlates strongly and significantly with the H i-to-stellar mass ratio and specific star formation rate, but not with the stellar mass, MH i, dark matter mass, or star formation rate. The strongly tidal-interacting galaxies tend to show deviations from these trends and have the most flattened profiles. These results imply that, in the absence of major tidal interactions, physical processes must cooperate so that ΣH i distributes in a self-similar way in the outer region down to the 0.01 M⊙ pc−2 level.