Origin and Evolution of Quasar Absorption Systems and Primordial Galaxies

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We have investigated galaxy formation/evolution processes by focusing on quasar absorption systems. In particular, we have explored the evolution of Damped Lyman-alpha(DLA) absorption system which contains most amount of neutral hydrogen in the universe. Specifically, we aim to reveal the mass and spatial distribution of neutral hydrogen gas, giving rise to DLAs, in a purpose to put constraints on an early stage of galaxy evolution.Our main results are as follows:(1) At low redshift(z～0), DLA galaxies(typical size～3 kpc), where the HI column densities are as high as those of DLA systems, contribute significantly to the population of HI-selected galaxies at neutral hydrogen mass 10^8 M(solar). We find a tight correlation between cross sections of HI gas and HI masses. This result based on our theoretical models is consistent with the blind radio observations.(2) At high redshifts(z> 2), DLAs are associated with gas in star-forming regions under an early stage of galaxy(e. g., Lyman-alpha emitter) evolution. Our result of DLA galaxy surveys using the adaptive optics system puts constraint on an upper limit of the star formation rates of 20 M(solar) yr^-1.Further investigation based on statistically significant sample size is required by carrying out both blind radio and optical/infrared surveys for DLA galaxies.