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SImulation of the epoch of reionziation : radiative transfer

Abstract : The 21-cm hyperfine line of neutral hydrogen from the high-redshift Universe (6 < z < 20) promises to probe a new era in cosmology, the epoch of reionization (EoR). It will provide more detailed, less ambiguous and more complete three-dimensional informations than other observations of the EoR (such as the QSO absorption lines, or the secondary scattering of CMB). It also traces many different physical processes. The next generation radio telescopes, SKA and its precursors, will start to operate within one decade, and will observe this signal. Numerical simulations predicting the 21-cm emission are important to optimize the design of the instruments, and interpret the observations.
In this work, we develop a continuum radiative transfer part for the LICORICE cosmological code to study the epoch of reionization, where radiative transfer is an essential tool. We use a Monte-Carlo ray-tracing algorithm on an adaptive grid. Several tests, both for static density field cases and radiative hydrodynamic cases have been performed to validate the code.
Then we compute the 21-cm signal during the EoR, which provides a direct probe on reionization and contains a lot of informations on the sources of ionization and heating. Usually the Ly-α flux, which influences the strength of the 21-cm signal, is assumed to be strong and homogeneous during the whole cosmic reionization, but this assumption is not valid during the early stage of EoR. We evaluate exactly the local Ly-α flux using the Lyman line radiative transfer module of LICORICE and show that using the local Ly-α flux modifies the power spectrum of the 21-cm signal, especially during the early reionization. We also find a strong signal in absorption which can not be predicted with the usual assumptions.
Even a small amount of X-rays can affect the physical state of the neutral inter galactic medium since X-rays have a very long mean free path. X-ray heating is an important factor to evaluate the strength of the 21-cm signal in the neutral regions, so we implemented the corresponding ray-tracing in LICORICE. We find that X-rays need time to increase the gas temperature in the IGM above the CMB temperature, so with a reasonable level of X-rays we can still see the signal in strong absorption during the early phase of reionization.
In addition, we study the formation of galaxies in a cosmological context. The goal is to explore the physics of primordial galaxies considering radiative feedback on hydrodynamics. In a preliminary way, we find that including non-equilibrium ionization modifies the temperature of the diffuse gas, and its accretion history.
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Contributor : Sunghye Baek <>
Submitted on : Tuesday, September 22, 2009 - 3:47:28 PM
Last modification on : Thursday, December 10, 2020 - 12:36:27 PM
Long-term archiving on: : Tuesday, June 15, 2010 - 10:10:04 PM


  • HAL Id : tel-00419080, version 1


S. Baek. SImulation of the epoch of reionziation : radiative transfer. Astrophysics [astro-ph]. Institut d'Astrophysique de Paris, 2009. English. ⟨tel-00419080⟩



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