The imprint of the ionized intergalactic medium on the temperature anisotropy of the cosmic microwave background and the mutual-impact of reionization and small-scale structure
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Ionized intergalactic medium (IGM) is an important component in cosmic history. After recombination, the universe went though a dark age 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 current and future experiments can measure. In this dissertation, we discuss both of each aspects about ionized gas. First, we discuss the mutual-impact of reionization and the IGM in small-scale structures. While reionization took place preferentially from densest regions of the universe, IGM in average density regions is expected to have been ionized externally by galaxies formed in denser regions. Until ionized by external radiation, the IGM is expected to have grown numerous small-scale structures. We simulate how the hydrodynamic feedback on the small-scale structures and its impact on recombination. Then, we also discuss our result on how recombination can impact on the global progress of the reionization. Compared to previous works, we improve on the resolution of simulation. Previous studies took into account only the structures that can form in photoionized gas down to 10⁸ M [sun symbol] in mass. Here, we present a study that resolves halos down to 10⁴ M [sun symbol] to account for structures that were able to form before the reionization heats the gas. Second, we discuss the kinetic Sunyaev-Zel'dovich effect on the Cosmic Microwave Background (CMB) : temperature fluctuations via the Doppler shift induced by the line-of-sight (LOS) component of the momentum of electrons in the ionized IGM. For the EoR contribution to the signal, we calculate the 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 (10⁸ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁹ M [sun symbol]) and minihalos (10⁵ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁸ M [sun symbol]) is suppressed if these halos form in regions that are already ionized or Lyman-Werner dissociated. For the post-reionization signal, we revisit the currently used model for non-linear transverse momentum power spectrum with a particular emphasis on the connected term that has been neglected in the literature.