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

由于斯隆数字天文测量(以下简称SDSS)的望远镜和探测器的建造工作直到1998年6月才完成，我无法通过SDSS获得任何数据。我用Keck望远镜和气泡望远镜的观测数据来研究类星体吸收线系统的统计研究。我研究的第一个问题是CIV系统和受阻Lymanα系统的金属丰度，主要是利用Keck望远镜的高分辨率光谱结果。在假定光致电离模型的情况下，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。这解决了关于吸收系统化学演化的长期争论。二是莱曼阿尔法云的演化特征。气泡空间望远镜使观测莱曼阿尔法森林在低红移时成为可能，并提出了一个显著的结果，即莱曼阿尔法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。如果云的演化受漫射UV背景辐射的控制，则当UV辐射的峰值出现在z=1时，则重现Lymanα森林的数密度演化。这一结果表明，低红移时UV辐射的主要贡献者是年轻星系。解释莱曼阿尔法云在低红移时缓慢演化的另一种可能性是，由于时间尺度为3GY的相互碰撞，云的数量减少了。如果这是真的，这些云层可以归功于星系作为基石的等级形成。

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.