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

由于斯隆数字巡天（以下简称SDSS）的望远镜和探测器直到1998年6月才建成，我无法通过SDSS获得任何数据。我利用Keck望远镜和Bubble空间望远镜的观测数据代替SDSS，对QSO吸收线系统进行了统计研究。我探索的第一个问题是CIV系统和阻尼Lyman α系统的金属丰度，主要是利用凯克望远镜的高分辨率光谱结果。假设光电离模型，我们计算了上述吸收体系的电离状态，并将其与高红移观测结果进行比较，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表明的那样特别丰富。这解决了长期以来关于吸收系统化学演化的争议。第二个是莱曼α云的演化特征。气泡空间望远镜使得在低红移时观测莱曼α森林成为可能，并给出了一个显著的结果：莱曼α森林在低红移时不随时间减少，而在高红移时迅速减少。如果云的演化受漫射UV背景辐射控制，则在UV辐射峰值达到z=1时再现Lyman α森林的数密度演化，而通常不采用z=2。这一结果表明，低红移紫外线辐射的主要贡献者是年轻的星系。另一种解释莱曼α云在低红移时缓慢演化的可能性是，由于3 Gy时标的相互碰撞，云数减少。如果这是真的，那么这些云就会作为积木，为星系的分层形成做出贡献。

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.