Abstract

The Epoch of Reionization is the last major phase transition of the Universe, marking the passage from a completely neutral to a fully ionized intergalactic medium. This transition is driven by young star-forming galaxies that are reionizing their surrounding gas. Today, substantial observational effort is focused on observing the 21cm signal of the intergalactic neutral hydrogen that is being reionized and the galaxies driving the reionization. To help guide this observational effort predictions of the possible observations are being made, to asses the best observational strategies and possible synergies between different instruments. With this thesis, I am joining these efforts by focusing on three particular problems. I focus on possible synergies between ongoing observations of LOFAR and HSC that are going to observe 21cm emission and Lyman-alpha emitting galaxies respectively, as well as synergies between the next-generation survey SKA, observing the 21cm signal, and HSC, PFS, and WFIRST observing the galaxies. I show that cross-correlation between LOFAR and HSC observations should show an anti-correlation on the largest scales and thus prove that the signal LOFAR is observing, as a first-generation instrument, is indeed from the Epoch of Reionization. Cross-correlations between SKA and HSC can improve on this effort and combined with the synergy between SKA and WFIRST even show the evolution of this cross-correlation. I also focus on showing that SKA could potentially observe 21cm line-of-sight one-dimensional power spectra, which would give insight on cosmological small scales. Unlike the two- and three- dimensional observations which focus on large scales. I also examined the best possible observational strategies for SKA's two-dimensional observations, showing that observing perpendicular to line-of-sight would be much better than observing in direction of line-of-sight due to orders of magnitude smaller noise in angular direction than in frequency direction. Lastly, I focus on our theoretical understanding of the 21cm forest. I show that when it comes to supernovae feedback, when implemented in such a way not to change the reionization history as opposed to without implementing it, no statistical changes are found in the features of the 21cm forest spectra. I also confirmed that the changes in the resolution of simulations used to build the 21 cm forest spectra induced the most changes in the spectra. I show that LOFAR could observe the most prominent features in a 21cm forest spectra from likes of Cygnus A high-redshift radio loud source, with a signal to noise ratio S/N around 20. SKA, instead, could observe even the smallest features, with S/N around 200.