Probing reionization and early structure formation

Theoretical estimates agree that the first astrophysical objects in the Universe appeared when its age was a few hundred million years. Observations of the cosmic microwave background and distant quasars indicate that within the subsequent few hundred million years, the majority of cosmic hydrogen was ionized. Nevertheless, agreement has yet to be reached concerning the details of this reionization process, and the nature of the first objects, as well as how they interacted with their environment and influenced subsequent generations of astrophysical objects. Work presented in this thesis attempts to shed light on some of these issues and provide insight into the interpretation of future observations. Specifically, we study the usefulness of distant, early sources in constraining the mean neutral fraction of hydrogen, as well as other quantities of interest. We apply a simplified version of our analysis to the quasar SDSS J1030+0524, and obtain the strongest limit to date of the neutral fraction at early times, when the Universe was one billion years old. Our method also provides the ionizing flux and spectral shape of the quasar as well as the size of its ionized region. In addition, we quantify constraints on small-scale density fluctuations obtainable from distant gamma-ray bursts, such as those currently being detected by the Swift satellite. We calculate the distribution of distant supernovae and quantify its usefulness in probing reionization. Finally, using numerical cosmological simulations, we statistically investigate the feedback effects of ultraviolet radiation on the population of early protogalaxies.