1998 Fiscal Year Final Research Report Summary
Statistical Study of QSO Absorption Lines Based upon the Digital Sky Survey
| Project/Area Number |
08454052
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | Nagoya University (1997-1998)
Osaka University (1996) |
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Principal Investigator |
IKEUCHI Satoru Nagoya University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (90025461)
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| Project Period (FY) |
1996 – 1998
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| Keywords | QUASAR (QSO) / Intergalactic Clouds / Diffuse UV Radiation / Lyman Alpha Forest / Formation of Galaxies / Metal Abundance |
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| Research Abstract |
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.
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