Cosmic Lighthouses : unveiling the nature of high-redshift galaxies

We are in the golden age for the search for high-redshift galaxies, made possible by a combination of new instruments and innovative search techniques. One of the major aims of such searches is to constrain the epoch of reionization (EoR), which marks the second major change in the ionization state of the Universe. Understanding the EoR is difficult since whilst it is galaxy evolution which drives reionization, reionization itself influences galaxy evolution through feedback effects. Unraveling the interplay of reionization and galaxy evolution is further complicated by of a lack of understanding of the metal enrichment and dust distribution in high redshift galaxies. To this end, a class of galaxies called Lyman Alpha Emitters (LAEs) have been gaining enormous popularity as probes of all these three processes. In this thesis, we couple state of the art cosmological SPH simulations (GADGET-2) with a physically motivated, self-consistent model for LAEs, so as to be able to understand the importance of the intergalactic medium (IGM) ionization state, dust and peculiar velocities in shaping their observed properties. By doing so, the aim is to gain insight on the nature of LAEs, put precious constraints on their elusive physical properties and make predictions for future instruments such as the Atacama Large Millimeter Array (ALMA). Using our LAE model in conjunction with a code that builds the MW merger tree (GAMETE), we build a bridge between the high-redshift and the local Universe. We also use SPH simulations (GADGET-2) to study the nature of the earliest galaxies that have been detected as of yet, place constraints on their contribution to reionization, and predict their detectability using the next generation of instruments, such as the James Web Space Telescope (JWST).