AI 中文总结
该研究基于FAST全天氢原子巡天第二次数据发布，构建含132个低红移氢原子吸收体的大同质样本，揭示其特性，为未来相关巡天建立基准。
AI 中文摘要
我们基于FAST全天氢原子巡天（FASHI）的第二次数据发布（FASHI DR2），开展了一项针对氢原子21厘米吸收系统的非目标巡天，覆盖约19500平方度，红移z≤0.09。共识别出132个氢原子吸收体，其中约60个为新发现，构成了迄今已汇编的最大的低红移氢原子吸收体同质样本之一。该样本可探测到低至2.6毫央斯基的连续谱流量密度，远低于此前流量限巡天的探测极限。吸收体群体以窄系统为主（W₅₀<100千米每秒），而宽吸收体（W₅₀>200千米每秒）占样本的13.6%。大多数吸收体为光学薄，其中值光学深度τ_HI≈0.14。速度偏移分布相对于宿主星系的系统速度大致对称。相关吸收体优先出现在大质量、正在积极形成恒星的星系中。我们发现氢原子柱密度与恒星质量之间存在弱反相关的初步证据，尽管该关系存在显著离散性。这些结果基于FASHI DR2样本首次对低红移氢原子吸收体群体进行了统计表征，并为下一代射电设备开展的未来氢原子吸收巡天建立了有价值的基准。
英文摘要
We present an untargeted survey of 21 cm HI absorption systems based on the second data release of the FAST All Sky HI survey (FASHI DR2), covering approximately 19,500 deg$^{2}$ at $z\lesssim0.09$. A total of 132 HI absorbers are identified, including approximately 60 new discoveries, forming one of the largest homogeneous samples of low-redshift HI absorbers assembled to date. The sample extends to continuum flux densities as low as 2.6 mJy, substantially below the limits of previous flux-limited surveys. The absorber population is dominated by narrow systems ($W_{50}<100$ km s$^{-1}$), while broad absorbers ($W_{50}>200$ km s$^{-1}$) account for 13.6% of the sample. Most absorbers are optically thin, with a median optical depth of $τ_{\rm HI}\approx0.14$. The velocity-offset distribution is broadly symmetric about the systemic velocities of the host galaxies. The associated absorbers are preferentially found in massive, actively star-forming galaxies. We find tentative evidence for a weak anti-correlation between HI column density and stellar mass, although the relation exhibits substantial scatter. These results provide the first statistical characterization of the low-redshift HI absorber population based on the FASHI DR2 sample and establish a valuable benchmark for future HI absorption surveys with next-generation radio facilities.
CommentsSubmitted to ApJS; under review after minor revisions
