Simulating reionization in numerical cosmology

Details Simulating reionization in numerical cosmology Simulating reionization in numerical cosmology

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt........10s&link_type=abstract

Thesis (PhD). HARVARD UNIVERSITY, Source DAI-B 64/05, p. 2229, Nov 2003, 262 pages.

Mathematics

Logic

Scientific paper

The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized. I present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by various sets of sources. The method requires relatively few time steps and can be employed with simulations of high resolution. First, I explore the reionization history of Helium II by z < 6 quasars. Comparisons between HeII opacities measured observationally and inferred from our analysis reveal that the uncertainties in the empirical luminosity function provide enough leeway to provide a satisfactory match. A property common to all the calculations is that the epoch of Helium II reionization must have occurred between 3≲z≲4 . I extend my analysis to study the constraints that can be placed on the nature of the cosmic ultraviolet (UV) background in the redshift interval 2.5≲z≲5 . I find that in order to simultaneously match observational estimates of the HI and HeII opacities, galaxies and quasars must contribute about equally to the ionizing background in HI at z ≃ 3. Moreover, my analysis requires the stellar component to rise for z > 3 to compensate for the declining contribution from bright quasars at higher redshift. To investigate how stellar source may have reionized the universe at z > 6, I have combined our 3D radiative transfer code with high resolution hydrodynamical simulations to study how population II and III type stars affected the reionization process. The resulting complex reionization histories are presented and comparisons made with observational constraints on the neutral fraction of hydrogen at z ˜ 6 derived from the z = 6.28 SDSS quasar of Becker and coworkers and the recent WMAP measurements of the electron scattering optical depth analysis of Kogut and co-workers.

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