Ph.D Student | Gleser Liron |
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Subject | Reionization from the Dark Ages until the Present |

Department | Department of Physics |

Supervisor | Professor Adi Nusser |

Full Thesis text |

Hydrogen reionization is the least understood process in the evolution of our Universe. However, major observational programs specifically designed to probe the Epoch of Reionization (EoR) are underway and are expected to provide data within the next few years. These programs are aimed to measure the 21-cm cosmological signal from the hyperfine structure transition in neutral hydrogen (H I) in the intergalactic medium (IGM).

In the first part of this PhD dissertation, we study the morphology of the total gas and the H I distributions during the EoR by means of Minkowski Functionals (MFs) of isodensity surfaces. The MFs of the total gas distribution are well described by the analytic expressions derived for lognormal random fields. The statistical properties of the diffuse H I depend on the gas distribution and on the way ionized regions propagate in the IGM. The deviations of the MFs of the H I distribution from those of a lognormal random field are, therefore, caused by reionization. We use the MFs to discriminate between the various stages of reionization and demonstrate the ability of MFs to distinguish between different reionization scenarios .

In the second part, we present a method for extracting the expected cosmological 21-cm signal from the EoR, taking into account contaminating radiations. The method is based on the maximum a-posteriori probability formalism and employs the coherence of the contaminating radiation along the line-of-sight and the three-dimensional correlations of the cosmological signal. We test the method using a detailed and comprehensive modeling of the cosmological 21-cm signal and the contaminating radiation, and show that a reliable recovery of the 3D cosmological signal is possible from noisy and foreground contaminated 21-cm maps .

In the third part, we leave the EoR, in which H I and He I are reionized, and study a late stage of reionization, in which the He II is reionized. We present a Monte Carlo model of He II reionization by quasars and its effect on the thermal state of the clumpy IGM. The model assumes that patchy reionization develops as a result of the discrete distribution of quasars. It includes various recipes for the propagation of the ionizing photons, and treats photo-heating self-consistently. The model predicts the fraction of He III, the mean temperature in the IGM, and the He II mean optical depth --- all as a function of redshift. It also predicts the evolution of the local temperature versus density relation during reionization .