Evolution Of IMBH & Mini-QSO's Contribution To Cosmic Reionization

The formation of the first generation objects and the cosmic reionization are very important problems in modern cosmology. According to the big-bang model, the universe at present is the evolution result of big-bang, inflation, nucleosynthesis, radiation decoupling with matter and so on. Based on the theory of gravitational instability of density perturbations, dark matter halos formed at later time after the linear growth stage and the spherical collapse stage, and the first generation of galaxies and stars finally formed in these dark matter halos. After that, the reionization of IGM due to these first generation objects began and would affect the formation of next generation of galaxies and stars. Besides, the reionization of IGM is also related to the evolution of high-redshift objects such as QSOs and black holes.Advances in both theory and technology, especially the launching of space telescopes, make it possible to validate the big-bang model and its predictions. However, the problems of when and how the universe was reionized are still uncertain. The observational data of the highest redshift QSOs imply that the IGM has been completely ionized at z～6, so we have to study higher redshift objects that beyond the work space of nowadays telescopes. Thanks to the rapidly improved computing technology, we can now use the numerical simulations to study the evolution of the universe at any high redshift.In this article, we focus on the issues of the formation of SMBHs, the mass growth of IMBH and the contribution of mini-QSOs (which are evolved from IMBHs) to the cosmic reionization. This article is based on theΛCDMcosmological model and arranged as follows: In chapter 1, we summarize the basic theory of the formation of first generation objects, the number density of dark matter halos, the cooling and collapse of gas, the formation and evolution of Pop III stars as well as the process and possible ionizing sources of reionization. Chapter 2 is mainly about by what way the mass of SMBH's'seed'black holes grow. In chapter 3, we focus on the relationship between the black holes'mass and the velocity dispersion of their host galaxies, i.e., the so-called M_BH-σ_* relation. In chapter 4 with the aid of numerical simulations, we illustrate how the IMBH grows and how they can fit the M_BH-σ_* relation. In chapter 5, we try to illustrate the contribution of mini-QSOs to the cosmic reionization. In chapter 6, we summarize and discuss the conclusions we obtained.Throughout this article, unless otherwise specified, the cosmological parameters are adopted from the 5 year WMAP data, i.e.,Ω_mh² = 0.1369,Ω_Λ= 0.721,Ω_b= 0.0462, h = 0.701,σ₈ = 0.817.