"Photon Budget for Ionizing Intergalactic Gas During Cosmic Reionization and Imprint of the Ionized Gas in the Cosmic Microwave Background"
Ionized gas is an important component in the cosmic history. After the recombination, the universe went though a dark age without any collapse structures to produce radiation until the first stars formed. Since the formation of the first stars, the ionized gas, on one hand, played an important role in the history of the universe and, on the other hand, left its imprints on observables that we current and future experiments can measure. In this thesis, we discuss one of each aspects about ionized gas.
First, we discuss how much recombination rate it made during the epoch of reionization. In order for early galaxies to achieve reionization of the universe, they have to produce a number of photons that is enough ionize intergalactic gas not only once, but more to make up for recombination in the ionized gas.
Compared to previous works, we improve on the resolution of simulations. Previous studied took into account only the structures that can form in the temperature of photo-ionized gas, 10,000 K, or down to 10^8 M_sun in terms of the mass of a halo. Here, we present a study that resolves halos down to 10^4 M_sun to account for structures that were able to form before the reionization heat the gas.
Second, we discuss the imprint of ionized gas in the Cosmic Microwave Background (CMB) induced by free electrons up-scattering CMB photons called the kinetic Sunyaev-Zel`dovich effect. For the signal coming from the Epoch of Reionization (EoR), we calculate expected signal from simulations of cosmic reionization that, for the first time, includes the effect of "self-regulation" of reionization: star formation in low-mass galaxies (10^8 M_sun <~ M <~ 10^9 M_sun) and minihalos (10^5 M_sun <~ M <~ 10^8 M_sun) is suppressed if these halos form in regions that are already ionized or Lyman-Werner dissociated. For the post-reionization signal, we revisit currently used model for the non-linear transverse momentum power spectrum with a particular emphasis on the connected term that has been neglected in the literature.
University of Texas at Austin