New H I Observations Toward the NGC 5055 Galaxy Group with FAST

We report a new high-sensitivity H I mapping observation of the NGC 5055 galaxy group over an area of 1.°5 × 0.°75 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our observation reveals that the warped H I disk of NGC 5055 is more extended than what was previously observed by WSRT, out to 23.'9 (61.7 kpc). The total H I mass of NGC 5055 is determined to be ∼1.1 × 10¹⁰ M _⊙. We identified three H I clouds with H I masses of the order of ∼10⁷ M _⊙ at the southeastern edge of the H I disk, as well as a candidate high-velocity cloud with an H I mass of (1.2 ± 0.5) × 10⁶ M _⊙ to the north of NGC 5055. The H I content of UGCA 337 is robustly detected for the first time by the FAST observations. It has a narrow H I linewidth of W ₅₀ = 17.4 ± 3.8 km s^‑1 with a total H I mass of (3.5 ± 0.3) × 10⁶ M _⊙. Comparing the gas content and g‑r color of UGCA 337 with typical low-mass dwarf galaxies, UGCA 337 appears relatively gas-poor despite its blue color. This suggests that UGCA 337 may have undergone gas stripping in the past. We also analyzed the possible origin of the diffuse H I clouds located at the outskirts of NGC 5055, and speculate that they might be the remnant features of a merger event in the past.