  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).
