Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 42 for “"reionization"”.
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Simulations of cosmic reionization
… photons emitted by stars in galaxies cause the reionization of the Universe, the transition during which most of the gas in the Universe from a mostly neutral, to a highly ionised state it is in today. To this end, we discuss and improve two techniques for the transport of ionising radiation …
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Decaying dark matter and reionization
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1993
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Illuminating the Universe : New Probes of Reionization and Cosmology
We model the epoch of hydrogen reionisation of the universe, using analytic as well as numerical methods. In a detailed statistical analysis of our results, we find good agreement in the alternative descriptions of the morphology of ionized regions. We use the simulations to make predictions for …
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Modelling the Epoch of Reionization with Cosmological Radiative Transfer Simulations
The epoch of reionization is the ionization of neutral hydrogen by UV photons emitted from the first sources. While its end is well constrained by Ly𝛼 forest observations, the timeline and contributing sources remain active research areas. In this thesis, I model reionization by post-processing a …
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Numerical Simulations of Galaxy Formation During the Epoch of Reionization
… in galaxy formation during the epoch of reionization and presents multiple new computational techniques developed specifically to study this era. This work naturally divides into two main sections: 1) The formation of the first massive black holes and 2) Interpreting ALMA observations of …
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The THESAN Project: ionizing escape fractions of reionization-era galaxies
… observational data, the sources driving reionization remain uncertain. In this work we calculate the ionizing escape fractions (𝑓 subscript esc) of reionization-era galaxies from the state-of-the-art THESAN simulations, which combine an accurate radiation-hydrodynamic solver (arepo-rt) …
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Unveiling the epoch of reionization by simulations and high-redshift galaxies
The Epoch of Reionization marks after recombination the second major change in the ionization state of the universe, going from a neutral to an ionized state. It starts with the appearance of the first stars and galaxies; a fraction of high-energy photons emitted from galaxies permeate into the …
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Lyα emission as a sensitive probe of galactic mergers and reionization
… has emerged as a powerful probe of the epoch of reionization. This thesis investigates how various physical processes shape Lyα emission and its connection to cosmic reionization, using state-of-the-art cosmological zoom-in simulations. By post-processing these simulations, we generate synthetic …
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Chasing ancient demons : tools for measuring 21 cm fluctuations before reionization
… measuring the fluctuations in HI emission before reionization which carry information on the first X-ray emitting compact objects and hot interstellar gas heated by the deaths of the first stars (ancient demons). First, we show that existing and planned interferometers are sensitive enough to …
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Probing the epoch of reionization with redshifted 21 cm HI emission
Emission and absorption features in the spectrum of the diffuse radio background below 200 MHz due to the 21 cm hyperfine transition line of neutral hydrogen gas in the high redshift intergalactic medium offer a new and potentially valuable probe into the evolution of the Universe during the poorly …
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Probing the early universe with the epoch of reionization and QSO spectroscopy
We present results from the first systematic survey for Mg ii absorption lines at z > 2.5. Using 46 infrared QSO spectra we discovered 111 Mg II systems, including five with z > 5- the most distant systems now known. The comoving line density for weaker systems is statistically consistent with no …
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Polarization and its Discontents: How Polarized Foregrounds Affect 21cm Epoch of Reionization Measurements
… and occured during what is called the Epoch of Reionization (EoR). The ionization history of the intergalactic medium can be directly measured by 21cm emission from the hyperfine transition of hydrogen. Measurments of the 21cm signal from the EoR can yield information about those first luminous …
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Robust Statistical Radio Interferometric Methods for the Detection of the Epoch of Reionization
… HI to constrain the properties of the Epoch of Reionization and to better understand the astrophysical and cosmological processes of the early Universe. The sensitivity requirements for such a detection are exacting, since astrophysical foregrounds overshadow the 21 cm signal by roughly five …
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Constraining reionization: Evidence from 21 cm limits and predictions for fast radio bursts
… on the properties of early galaxies, the reionization history, and the global 21 cm signal. Specifically, I use upper limits on the 21 cm power spectrum measured by the HERA interferometer, current and future measurements of the global 21 cm signal, and forecasts for high redshift Fast …
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Preliminary work for three-dimensional imaging of the epoch of reionization with interferometers
… model in the Dark Ages and the Epoch of Reionization via both the power spectrum and direct imaging [4]. In order to get three-dimensional images from calibrated inteferometer data, we develop a mapping algorithm called Direct Inversion Matrix (DIM) (151, [6]) that has many advantages …
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Understanding the Epoch of Reionization Using Simulations of Lyman-α Emitting Galaxies and 21-cm Emission
… of the Universe’s history known as the Epoch of Reionization (EoR). In this thesis I explore: (i) how we can use simulations to model the IGM transmission to LAEs during reionization, and what simulations reveal about the environmental dependence of this transmission. I use these simulations to …
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Probing the Intergalactic Medium with high-redshift quasars
Clues about the timing of reionization and the nature of the ionizing sources responsible are imprinted in the ionization and thermal state of the IGM. In this thesis, I use high-resolution quasar spectra in conjunction with state-of-the-art hydrodynamical simulations to probe the IGM at high …
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EoR in alternative cosmological scenarios
… that the observations related to the epoch of reionization can probe not only the evolution of the IGM state, but also the cosmological background in which this process occurs. In fact, the history of the IGM ionization is indeed affected by the evolution of the sources of ionizing photons …
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Studying the Large Scale Structure and interstellar Medium of Galaxies During the Epochs of Peak Cosmic Star formation and Reionization With Infrared Fine Structure Lines
… epochs of peak cosmic star formation (SF) and Reionization. Chapter 1 of this thesis is a study of the ISM of the Cloverleaf quasar. Observations of IR FS lines from singly ionized carbon and neutral oxygen have allowed us to assess the physical conditions—parametrized by their gas density and …
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Fundamental physics from observations of the early universe
… Universe. Inhomogeneities in recombination and reionization amplify the perturbations in the underlying matter density and the resulting second order effects may be important. I calculate the bispectrum due to these second order effects and find that they are not an important source of confusion …
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