2025ApJS..278...37Y

Using the Five-hundred-meter Aperture Spherical radio Telescope, we have performed an Ursa Major supergroup H I survey covering the entire UMa region centered at R.A. = 11^h59^m28$\mathop{.}\limits^{{\rm{s}}}$3, decl. = 49°05'18″ with a radius of 7$\mathop{.}\limits^{\unicode{x000B0}}$5. We have obtained the most complete catalog of H I sources in the UMa supergroup, containing 178 H I sources with velocities in the range 625-1213.4 km s^–1 and masses in the range 10^6.0-10^10.1M_⊙ assuming a distance of 17.4 Mpc. Among them, 55 H I sources were detected for the first time, of which 32 do not have known optical redshifts. For these 32 sources, we have searched the DESI Legacy Surveys and found optical counterparts for 25 of them (with optical images, but no redshifts), with the remaining seven sources being pure H I clouds without an optical counterpart. We detected H I distributions in some interacting systems and discussed four small groups in detail. We computed the neutral hydrogen mass function (H I MF) of the UMa supergroup using the 1/${V}_{\max }$ method and fitting it with the nonlinear least-squares (NLLS) and modified maximum likelihood (MML) methods. We obtained the following H I MF parameters: log₁₀(ϕ_*/Mpc^–3) = -0.78 ± 0.15, α = -1.05 ± 0.07, and log₁₀(M_*/M_⊙) = 9.87 ± 0.19 for the NLLS method, and log₁₀(ϕ_*/Mpc^–3) = -0.70 ± 0.11, α = -1.05 ± 0.05, and log₁₀(M_*/M_⊙) = 9.77 ± 0.13 for the MML method. This result is similar to that derived from the Very Large Array blind survey, but the slope is steeper because we detected more low-mass galaxies. The slope is flatter than that of the global H I MF, which agrees with the theoretical prediction that galaxies in high-density regions are stripped of gas due to interactions.