Study of Galaxy Evolution by Utilizing Absorption Systems of Quasars

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The physical properties and their evolutionary characteristics of quasar absorption systems have been studied, especially, in focusing to the Lyman alpha forest and metallic absorption lines.As for the Lyman alpha forest, several aspects such as the gravitational lensing effects, the dynamical evolution of minihalos, the explanation of HST results at z = 0-1 in relation to the time variation laws of diffuse UV background and interactions of minihalos with pervasive intergalactic medium. The conclusions are : (1) The intensity of diffuse UV flux decreases rapidly at z < 2 and increases/keeps constant at z > 2 with decreasing z. (2) According as this evolution law of diffuse UV flux, the minihalo as a model of Lyman alpha forest expands at z > 2 and then changes to contraction at z < 2 with time. (3) Due to the dynamical interactions with pervasive intergalactic medium, the HI gas in a minihalo is easily swept out and missed in detection. This explains the reason why the Lyman alpha fore … More st does not show any clustering features because minihalos are swiftly destructed if clustered.As for the metallic line systems, based upon a simple model for proto-galaxies with giant halos, the column densities of respective ions of C, Si, Mg, O and H have been calculated in consideration of the UV flux from young stars in a proto-galaxy as well as the diffuse cosmic diffuse UV background. For reproducing the observed characteristics of CIV and Lyman limit systems altogether, the intensity and spectral index of each UV flux and gas distribution laws in a protogalactic halo are deduced. These are consistent with those determined by other reasons.In addition to these respective models of absorption systems, it is examined whether the cosmological constant is needed to reproduce the observed number density and its evolution law of each ion. The result indicates that the cosmological constant is helpful for the observed number density behavior of MgII systems but not necessary for other absorption systems within present sparse data. It is crucial to observe nearby absorption systems by using the HST for giving much clearer conclusions on the cosmological constant. Less