1990 Fiscal Year Final Research Report Summary
Exploring the Far Distant Universe by Using Quasars as a Probe
| Project/Area Number |
01540224
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Astronomy
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| Research Institution | National Astronomical Observatory |
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Principal Investigator |
IKEUCHI Satoru National Astron. Obs., Division of Theoretical Astrophysics, Prof., 理論天文学研究系, 教授 (90025461)
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| Co-Investigator(Kenkyū-buntansha) |
TOMISAKA Kouji Niigata University, Faculty of Education Associate Prof., 教育学部, 助教授 (70183879)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Absorption Line Systems / Lyman alpha Forest / Lyman Limit Systems / Damped Lyman alpha Lines / Cold Dark Matter / Minihalos / Galaxy Formation / Diffuse UV Flux |
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| Research Abstract |
By utilizing the observational data such as III column density distribution and number density evolution laws of absorption line systems of quasars, I investigated the evolutionary features of young galaxies and diffuse UV flux at the red shifts of z = 0.3 - 4. In this research project, I concentrated to the following two categories : (1) CIV absorption line systems as a probe of galactic halos, and (2) three kinds of HI absorption systems as a probe of intergalactic clouds. Main conclusions are as follows.
As for the first category, I studied the dynamical behavior of a gasecous halo, the increasing rate of heavy element abundances and the time variation of diffuse UV flux utilizing the observational data. As a result, I concluded that the gaecous halo is rapidly expanding and the heavy element abundances are increasing fast during the red shift z = 3 to 2. On the other hand, I found the diffuse UV flux to be constant in this epoch. These conclusions indicate that young galaxies were s
… More
o active in star formation and gaseous halos dynamically expand to 100 kpc due to the intense energy ejection from stars. At the same time, the emission of UV light from galaxies largely contributes to the diffuse UV background.
As for the second category, I proposed a unified model for three kinds of III absorption systems, which are the Lyman alpha forest, Lyman limit systems and damped Lyman alpha line systems. The fundamental model is a minihalo which is an intergalactic cloud confined by the gravity of cold dark matter. This minihalo is ionized and heated up by the diffuse UV flux. Therefore, if the diffuse UV flux varies in time the evolution of minihalos is driven. In the envelope of a minihalo the gas is highly ionized and it is detected as the Lyman alpha forest. In the central part the UV flux is attenuated and the gas keeps in neutral. This region is observed as an Lyman limit system or damped Lyman alpha line system. Massive minihalos will collapse and evolve to galaxies, which are detected as the absorption systems of the first category.
Accordingly, I concluded that the whole absorption line systems are reproduced under the cold dark matter dominated universe. Less
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