(Georgia Institute of Technology, 2013-05-08)
Demchenko, Vasiliy Grigoriyvich
Using the N-body, adaptive mesh-refinement, ray-tracing code Enzo, we studied the escape fraction of ultraviolet radiation in the early universe. We obtained data from a simulated cube 1 Mpc across of the early universe during the period known as reionization. We studied the effects of various galaxy properties on the escape fraction of ionizing radiation over a redshift period of 7.2 < z < 15. Using the data, we looked at all-sky maps of the neutral hydrogen and electron density at approximately 637 million years after the Big Bang. We found that the ionizing radiation escapes anisotropically from dark matter halos. We then studied the how the escape fraction of ionizing radiation depends on dark matter halo mass. We found that the escape fraction begins to decrease as a function of mass. This led us to conclude that high-mass, high-luminosity galaxies are not a main source of ionizing radiation. Since these high-mass, high-luminosity galaxies are created when low-mass galaxies combine, we conclude that it is in fact low-mass, low-luminosity galaxies that are the dominant contributors of ionizing radiation. They are more abundant and have higher escape fractions of radiation, thus supporting our claim. We also looked at finer time fidelity for the last 80 million years of the simulation to discover more about the escape fraction of radiation. We found that the escape fraction can vary over short timesteps of several million years, which is short in the cosmological sense. We compared our findings to those of Hinshaw et al. 2012 for their nine-year WMAP data. Their findings show an epoch of reionization at a redshift of approximately z = 10. Our results suggest that the main drivers of this reionization are the low-luminosity galaxies that we have studied in this thesis.