New H I observations toward the NGC 5055 Galaxy Group with FAST

Abstract

We report a new high-sensitivity H\,{\sc i} mapping observation of the NGC~5055 galaxy group over an area of $1.5^\circ\times0.75^\circ$ with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our observation reveals that the warped H\,{\sc i} disk of NGC~5055 is more extended than what previously observed by WSRT, out to $ 23.9$ arcmin (61.7 kpc). The total \HI\ mass of NGC~5055 is determined to be $\rm\sim 1.1\times10^{10}\,M_\odot$. We identified three H\,{\sc i} clouds with H\,{\sc i} masses of the order of $\rm \sim 10^7\,M_\odot$ at the southeastern edge of the H\,{\sc i} disk, as well as a candidate high-velocity cloud with an H\,{\sc i} mass of \textcolor{blue}{$\rm (1.2\pm0.5) \times10^6\,M_\odot$} to the north of NGC~5055. The HI content of UGCA 337 is robustly detected for the first time by the FAST observations. It has a narrow HI linewidth of \textcolor{blue}{$W_{50}=17.4\pm3.8$ km s$^{-1}$} with a total \HI\ mass of \textcolor{blue}{($\rm 3.5\pm0.3)\times10^6\,M_\odot$}. 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 colour. This suggests that UGCA~337 may have undergone gas stripping in the past. We also analyzed the possible origin of the diffuse \HI\ clouds located at the outskirts of NGC~5055, and speculate that they might be the remnant features of a merger event in the past.