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中文摘要：
阻尼莱曼α吸收线系统（DLAs）是中性氢柱密度超过2×10^20 cm^-2的类星体吸收线系统。按照现有的观点,DLAs是高红移环境中星系及恒星形成的中性气体库,它们很可能是现今星系的前身。近20年来随着DLAs巡天观测的迅猛发展,尤其是SDSS巡天观测数据的释放,DLAs统计样本达到千计的量级,大大推动了DLAs的观测和研究。由于受到观测的某些限制,样本还有偏,尤其是缺少低红移DLAs,但是,通过大样本DLAs系统的研究,已经获得了有关宇宙中性气体演化的许多信息,如DLAs的数密度在高红移处（z〉1.5）是有演化的,但在低红移处基本不演化,从而确认了今天的星系形成于较高红移处。研究也发现DLAs对宇宙质量密度的贡献随红移的演化减弱,DLAs的中性氢气体柱密度分布函数与本地星系的中性氢柱密度分布函数十分相似等一些有趣的结论。着重介绍DLAs的基本知识以及20年来巡天的有关进展,包括DLAs的观测证认、统计特性等,并指出目前DLAs样本不完备的主要原因。
英文摘要：
Damped LymanαAbsorption systems（DLAs） are high column density gaseous systems（lg（N_（H I））20.2）,detected through their absorption lines in the optical spectra of quasars at up to relatively high redshifts（～5）.They are regarded as the reservoirs of neutral gas in the Universe.Their study constitutes a powerful means to investigate the properties of distant galaxies and intergalactic medium（IGM）.In this first one of the two review papers,we give a detailed introduction to the recent progress in DLAs surveys.The next will review the results and progress in cosmic abundances of chemical elements and galactic evolution based on DLAs surveys and researches. The first systematic search for DLAs was done by Wolfe et al.in 1986.This Lick survey has found 15 systems at a mean redshift of 2.5 along the line of sight of 68 QSOs.Later,a series of surveys found more DLAs absorbers,but most of them are biased towards high redshifts since surveys at low and intermediate redshifts are difficult due to the lack of UV observations.In the recent years,the number of DLAs has increased substantially,especially from Sloan Digital Sky Survey（SDSS）.After mining the thousands of QSOs spectra from SDSS,Prochaska et al.and Noterdaeme et al.have found 738 and 937 DLAs respectively,increasing by one order of magnitude the number of known DLAs.The large sample of DLAs has statistically derived and/or confirmed some important results about the properties of neutral gas evolution across the cosmic time. One of the important quantities of DLAs from these surveys is the frequency distribution function f（N,H I）.Early surveys show that this function can be described by a power law.But recent large sample surveys show that the slope of f（N,H I） is much larger at high column density（lg（N_（H I））21.5）.The whole shape can be well fitted by a double power law or Gamma-function. The large slope at high column density implies that the systems at large neutral column density are rare.On the other hand,the sha
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