中文摘要：

利用Arecibo射电望远镜40％的ALFALFA（Arecibo Legacy Fast Arecibo L—band Feed Array）河外中性氢巡天数据，探讨了进行中性氢吸收线“盲寻”的过程与方法，并给出了搜寻吸收线的一些初步结果：（1）探测到的中性氢吸收源的数量共有10个，其中5个为文献中已知源，其余新发现的吸收线源需要进一步的研究与证实．（2）利用探测灵敏度给出了探测区域中性氢柱密度的上限，这些上限的频率统计分布显示阻尼莱曼＆吸收线系统（DLAs）中的中性氢气体的平均自旋温度与覆盖因子的比值E／，很可能大于500K．射电干扰与驻波是影响Arecibo河外中性氢吸收线探测的两个重要因素，也将进行一定的分析以及讨论相应的解决方法等．正在建设中的500m口径射电望远镜FAST（The Five-hundred—meter Aperture Spherical Telescope）与Arecibo射电望远镜属于相似类型，但在灵敏度、频带宽度、观测天区范围等方面都将有较大的提高，结合目前的研究进展对将来FAST在中性氢吸收线方面的研究也给出了一定的展望．

英文摘要：

We present some preliminary results of an on-going study of the HI 21- cm absorption line based on the 40~ data release of the Arecibo Legacy Fast Areeibo L-band Feed Array （ALFALFA） survey. Ten HI absorption candidates have been de- tected. Five of them are previously published in the literature, and the rest of them are new detections that need further confirmation. For those sources with no detected absorptions, we calculated the upper limits of their foreground HI column density NHI. The statistical result of the NHI distribution indicates that the ratio of average spin tem- perature to covering factor Ts/f for DLAs （the damped Ly~ systems） might be larger than 500 K. Radio frequency interference （RFI） and standing waves are the main issues affecting the detection of HI absorption profiles. Our study can serve as the pathfind- er for a large scale search of HI 21-cm absorption lines using the Five-Hundred-Meter Aperture Spherical Radio Telescope （FAST） which is an Arecibo-type radio telescope currently under construction in China. We discuss two types of observational studies of HI absorptions toward extragalactic sources using the FAST telescope.