标题： HI 21厘米吸收与类星体上的前景星系有关 显示英文标题

标题： HI 21-cm Absorption Associated with Foreground Galaxies on Top of Quasars

摘要： 对类星体-星系对（QGPs）中的HI 21厘米吸收进行系统搜索，为绘制高红移恒星形成星系周围的冷气体分布提供了一种强有力的方法。 高红移类星体的光纤光谱能够偶然探测到极小影响参数的前景恒星形成星系，从而形成一个独特的QGP子集，称为“类星体上的星系”（GOTOQs）。 在这项研究中，我们展示了针对三个GOTOQs的试点升级巨型米波射电望远镜（uGMRT）巡天的结果，在这次巡天中，我们实现了HI 21厘米吸收的100%检测率。 通过结合我们的发现与现有文献，我们确定了GOTOQs在HI 21厘米吸收方面构成了一个独特的群体，其检测率显著高于基于Damped Lyman-$\alpha$（DLA）或金属吸收的搜索所观察到的检测率。 对于GOTOQs，我们发现视线消光和HI 21厘米光学深度之间存在强烈的相关性，其特征由$\int \tau\, dv\, (\rm{km\,s^{-1}}) = 13.58^{+2.75}_{-2.35} E(B-V) + 0.68^{+1.06}_{-1.27}$描述，这与银河系视线一致。 我们还表明，HI 21厘米的检测率和光学深度随着影响参数迅速下降。 由于即将进行的广域光谱巡天有望大幅扩展已知GOTOQs的目录，这项试点调查的成功为构建具有统计意义的干预HI 21厘米吸收体样本奠定了基础。 显示英文摘要

摘要： A systematic search for HI 21-cm absorption in Quasar-Galaxy Pairs (QGPs) provides a powerful means to map the distribution of cold gas around high-redshift star-forming galaxies. Fiber spectroscopy of high-redshift quasars enables the serendipitous detection of foreground star-forming galaxies at extremely small impact parameters, forming a unique subset of QGPs known as Galaxies On Top Of Quasars (GOTOQs). In this study, we present results from a pilot upgraded Giant Metrewave Radio Telescope (uGMRT) survey of three GOTOQs, where we achieved a remarkable 100\% detection rate of HI 21-cm absorption. By combining our findings with existing literature, we establish that GOTOQs constitute a distinct population in terms of HI 21-cm absorption, with significantly higher detection rates than those observed in Damped Lyman-$\alpha$ (DLA)-based or metal absorption-based searches. For the GOTOQs, we find a strong correlation between the line-of-sight reddening and the HI 21-cm optical depth, characterized by $\int \tau\, dv\, (\rm{km\,s^{-1}}) = 13.58^{+2.75}_{-2.35} E(B-V) + 0.68^{+1.06}_{-1.27}$, consistent with the Milky Way sightlines. We also show that the HI 21-cm detection rates and optical depth declines rapidly with the impact parameter. With upcoming wide-field spectroscopic surveys expected to substantially expand the catalog of known GOTOQs, the success of this pilot survey lays the foundation for constructing a statistically significant sample of intervening HI 21-cm absorbers.