2025/10/27 by Yan, Shulan, Ma, Andrew, Yu, Qingzheng +3
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.22902
We investigate the atomic gas (HI) content of galaxies in groups using early data from the FAST All Sky HI survey (FASHI). Taking advantage of FAST's blind, wide-area coverage and uniform sensitivity, we assemble a sample of 230 group galaxies belonging to 182 groups at z≤0.03. These groups were identified using a halo-based group finder, and they have an median membership of 4 galaxies. We also derived a matched control sample of isolated systems, and apply censored-data modeling to include both detections and non-detections. At fixed stellar mass and color, we find that the global median HI fraction of group galaxies differs from that of controls by only -0.04 dex (95% CI [-0.18, 0.16]), indicating at most a mild average offset. The signal is not uniform across populations: satellites are HI-poor (median ΔfHI=-0.12 dex), whereas centrals are not HI-deficient (median ΔfHI=0.13 dex). Group galaxies located within 0.5R180 and in denser systems (richness >10 or local density Σ>10 \mathrmgal Mpc-2) show stronger negative offsets, whereas galaxies in the outskirts are statistically indistinguishable from the controls. These results refine earlier reports of global group HI deficiency: with deeper blind data and uniform treatment of upper limits, we show that HI depletion is primarily confined to satellites and compact cores rather than being ubiquitous across groups.