We present the early science results from a blind search of the extragalactic HI 21-cm absorption lines at z $\leqslant$ 0.09 with the drift-scan observation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We carried out the search using the data collected in 643.8 hours by the ongoing Commensal Radio Astronomy FasT Survey (CRAFTS), which spans a sky area of 3155 deg$^{2}$ and covers 44827 radio sources with a flux density greater than 12 mJy. Due to the radio frequency interference (RFI), only the relatively clean data in the frequency range of 1.3-1.45 GHz are used in the present work. Under the assumption of $T_{s}/c_{f}$ = 100 K, the total completeness-corrected comoving absorption path length spanned by our data and sensitive to Damped Lyman $α$ Absorbers (DLAs) are $ΔX^{inv}$ = 8.33$\times10^3$ ($Δz^{inv} = 7.81\times10^{3}$) for intervening absorption. For associated absorption, the corresponding values are $ΔX^{asc}$ = 12.8 ($Δz^{asc} = 11.9$). Three known HI absorbers (UGC 00613, 3C 293 and 4C +27.14) and two new HI absorbers (towards NVSS J231240-052547 and NVSS J053118+315412) are detected blindly. We fit the HI profiles with multi-components Gaussian functions and calculate the redshift (0.063, 0.066), width, flux density, optical depth and HI column densities for each absorption. Our results demonstrate the power of FAST in blindly searching HI absorbers. For absorption towards NVSS J231240-052547, the optical counterparts are faint and currently lack existing spectra. The most likely interpretation is that a radio-loud active galactic nucleus (AGN) is faint in the optical as the background source, with a faint optical absorber in between. NVSS J053118+315412 exhibits an associated absorption with a complex profile, which may suggest unsettled gas structures or gas accretion onto the supermassive black hole (SMBH).
The FAST HI 21-cm Absorption Blind Survey. III. OH Absorption Search in the 21-cm Absorber Sample and Continued HI Absorption Search
State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Department of Physics and Astronomy, University of the Western Cape（西开普大学）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学）；Key Laboratory of Cosmology and Astrophysics (Liaoning) & College of Sciences, Northeastern University（东北大学）；Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado（科罗拉多大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Research Center for Intelligent Computing Platforms, Zhejiang Laboratory（浙江实验室）；First Light Fusion Ltd.（第一光聚变有限公司）；ATNF, CSIRO Space and Astronomy（澳大利亚联邦科学与工业研究组织空间与天文天文台）；Sydney Institute for Astronomy, School of Physics A28, University of Sydney（悉尼大学）
Discovery of a 21 cm absorption system at z=2.327 with CHIME
University of British Columbia（不列颠哥伦比亚大学）；McGill University（麦吉尔大学）；Arizona State University（亚利桑那州立大学）；Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada（加拿大国家研究委员会赫茨伯格天文学与天体物理学研究中心 Dominion 射电天文台）
$\mbox{H}$ $\mbox{I}$ 21-cm Absorption Spectra Classification using Machine Learning
Indian Institute of Science Education and Research (IISER) Tirupati（印度科学教育研究所提鲁帕蒂分校）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: II. Program Design, Absorption-line Measurements, and Absorber Statistics
深星系调查显示，宇宙中的全球恒星形成率（SFR）密度在1 < z < 2时达到峰值，并在z = 0时急剧下降。但是，一个清晰的基本过程，特别是冷原子（~100 K）和分子气相的演变，驱动这样一个强大的演变尚未出现。MALS的设计目的是使用MeerKAT的L波段和UHF波段接收器，对0 < z < 2处的HI 21-cm和OH 18-cm吸收线进行最灵敏的（N（HI）>10 $^{19}$ cm $^{-2}$）尘埃无偏搜索。这将为星系冷原子和分子气体截面的演化提供可靠的测量，并揭示驱动SFR密度急剧演化的过程。从调查中获得的HI和OH吸收剂的大样本将（i）导致物理学的基本常数的最严格的约束，和（ii）是理想的适合于通过塞曼分裂或旋转测量合成探测星系盘中的磁场的演变。该调查还将提供HI和OH吸收剂的无偏普查，即在0 < z < 2时与强大AGN（>10 $^{24}$ W Hz $^{-1}$）相关的冷气体，并将同时提供盲HI和OH发射线调查和无线电连续谱调查。在这里，我们描述的MALS调查设计，观测计划和科学问题下，要解决的各种科学主题。
Quasar Sightline and Galaxy Evolution (QSAGE) Survey - I. The Galaxy Environment of OVI Absorbers up to z=1.4 around PKS 0232-04
我们提出的第一个结果，从OVI吸收星系周围的研究在$z<1.44$使用的数据从近红外棱镜光谱哈勃太空望远镜大计划，类星体视线和星系演化（QSAGE）调查。QSAGE是$z\sim1$的第一个专注于环星系介质的棱镜星系巡天，提供了对星系群的盲测。使用12个字段中的第一个字段，我们提供了减少方法的细节，特别是使用多个位置角度来最大限度地减少重叠痕迹污染影响的深棱栅数据的处理。得到的星系样本是H $α$通量受限的（$f({\rm Hα}) > 2\times10^{-17}$ erg s $^{-1}$ cm $^{-2}$），0.68<z<1.44，对应于$\gtrsim0.2-0.8$ M $_\odot$ yr $^{-1}$。我们结合银河系数据和背景类星体的高分辨率STIS和COS光谱来研究环银河系介质中的OVI。在z>0.68时，我们发现了5个OVI吸收系统，它们的碰撞参数为$b\approx100-350$ kpc（proper），而另外13个星系在相同的碰撞参数和红移范围内没有明显的OVI吸收（即$N({\rm OVI})<10^{13.5-14}$ cm $^{-2}$）。我们发现一个大的分散在恒星质量和恒星形成率的最近的星系与相关的OVI。虽然OVI吸收剂系统之一被发现与$z\approx1.08$的低质量星系群有关，但我们推断检测到的OVI吸收剂通常位于质量为$10^…
