Evolution of Galaxies and the intergalactic medium at high redshift

Abstract

Research presented in this thesis follows two threads in the broad area of cosmology: (1) properties of the intergalactic medium (IGM), and (2) formation of galaxies and their evolution. Mainly from observations of absorption systems in high-redshift quasar spectra, the intergalactic medium has been inferred to be ionized, as well as chemically enriched, up to redshift of about six. This effect is termed reionization. It has been the focus of large amount of research in the last decade. With this in mind, this thesis deals with the following issues: (1) the problem of constraining early star formation from reionization-related observations; and (2) developing selfconsistent models of reionization and suggesting new observables. Apart from these two issue, we also look at galaxy formation in greater detail in this thesis. Understanding how observed small scale structure, including galaxies, can emerge in the well-accepted Cosmological Constant-Cold Dark Matter (LCDM) cosmological model is an important open problem. This thesis includes (1) predictions for the evolution of the neutral hydrogen content in galaxies and its large-scale distribution in the universe over a range of redshifts, and (2) a study of assembly of supermassive black holes in nuclei of high redshift galaxies. In the first component of this thesis, we use a simplified approach for studying formation of stars in collapsed haloes, and the resulting ionization and enrichment of the IGM. We consider a set of LCDM models allowed by observations and constrain parameters related to star formation with the help of the observed IGM metallicity and its Thomson scattering optical depth. We find that a ?normal? initial mass function (IMF) may satisfy these two constraints. Observations require a significant fraction of metals to escape from haloes to the IGM.