Simulating the spectra of galaxies in the reionization epoch : Constraining the escape fraction of ionizing photons

Abstract: The cosmic reionization represents a fundamental yet poorly understood phase transition in the evolution of our universe. The most promising theory is that the ionizing radiation from young hot stars in star-forming galaxies drove reionization, but much information about the number of galaxies and the escape fraction of ionizing radiation from galaxies is still missing. In this thesis, I discuss a technique for estimating the escape fraction of hydrogen ionizing radiation from galaxies in the reionization epoch. The method utilizes the power law slope of the UV continuum and the equivalent width of the Balmer beta emission line to try to estimate the escape fraction of a galaxy from its spectrum without ever directly observing any ionizing radiation. The technique is applied to simulated galaxies from large scale cosmological simulations.I find that the method works for estimates of the escape fraction of dust free simulated galaxies. It is possible to distinguish between galaxies with escape fractions 0.0, 0.5, 0.7 and 0.9 when no dust is added to the galaxies. I also show that the method works regardless of choice of numerical assumptions and assumptions about stellar evolution in the models. Lastly, I show that the addition of dust to the galaxies can introduce an ambiguity to the estimated escape fraction, and that this may reduce the estimation into just being between high or low escape fractions. The results also show that equivalent widths of the Balmer beta emission line larger than approximately 100 Ångströms are seen only in galaxies with escape fractions consistent with zero. The addition of dust and its effect on the spectral features used in the technique allows for an estimation of the average dust content. I find that the galaxies contain low amounts of dust, with a highest average dust attenuation in the visual of A=0.4-0.6 magnitudes.