Statistical Study of QSO Absorption Lines Based upon the Digital Sky Survey

由于斯隆数字巡天（Sloan Digital Sky Survey，以下简称SDSS）的望远镜和探测器的建设直到1998年6月下旬才完成，无法通过SDSS获得任何数据，因此我用凯克望远镜和气泡空间望远镜的观测数据代替SDSS，对类星体吸收线系统进行了统计研究。第一个探索的问题是CIV系统和阻尼莱曼α系统的金属丰度，主要利用凯克望远镜的高分辨光谱结果。在光电离模型的假设下，我们计算了上述吸收体系的电离态，并与高红移下的观测结果进行了比较，以了解C和Si的电离结构和丰度。我们的研究结果表明，这些金属元素并不像以前的研究所表明的那样特别丰富。这解决了长期存在的争议的化学演变的吸收系统。二是莱曼α云的演化特征。气泡空间望远镜使得观测低红移的莱曼α森林成为可能，并提出了一个显着的结果，即莱曼α森林在低红移时不随时间而减少，而在高红移时则迅速减少。如果云的演化是由漫射紫外背景辐射控制的，那么当紫外辐射峰值出现在z=1时，云的数密度演化再现了莱曼α森林的数密度演化，而通常不采用在z=2时。这一结果表明，在低红移的紫外辐射的主要贡献者是年轻的星系。另一种解释低红移时莱曼α云缓慢演化的可能性是，云的数量减少是由于时间尺度为3戈伊的相互碰撞。如果这是真的，这些云就有助于星系作为积木的等级形成。

Since the construction of telescopes and detectors for Sloan Digital Sky Survey (hereafter, SDSS) has not been completed till the last June of 1998, I could not get any data through SDSS.In place of SDSS, I used the observational data by Keck telescope and Bubble space telescope for investigating the statistical study of QSO absorption line systems. The first problem which I explored is the metal abundance of CIV systems and damped Lyman alpha systems, mainly using the high resolution spectroscopic results by Keck telescope. Assuming the photo-ionization model, we calculated the ionization states of the above absorption systems and compared them with observational results at high redshifts in order to see the ionization structures and abundances of C and Si. Our results show that these metal elements are not specially abundant as indicated by previous studies. This resolves the long standing controversy of chemical evolution of absorption systems. The second one is the evolutionary features of Lyman alpha clouds. Bubble space telescope made possible to observe the Lyman alpha forest at low redshifts and presented a remarkable result that the Lyman alpha forest does not decrease with time at low redshifts in contrast to the rapid decrease at high redshifts. If the evolution of clouds is controlled by the diffuse UV background radiation, the number density evolution of Lyman alpha forest is reproduced if the peak of UV radiation attains at z=1, not usually adopted at z=2. This result indicates the main contributors to UV radiation at low redshifts are young galaxies. Another possibility for explaining the slow evolution of Lyman alpha clouds at low redshifts is that the cloud number decreases due to mutual collisions with the timescale of 3 Gy. If this is true, the clouds cntribute to the hierarchical formation of galaxies as building blocks.