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Abstract: We study the topology of reionization using accurate three-dimensionalradiative transfer calculations post-processed on outputs from cosmologicalhydrodynamic simulations. In our simulations, reionization begins in overdenseregions and then -leaks- directly into voids, with filaments reionizing lastowing to their combination of high recombination rate and low emissivity. Thisresult depends on the uniquely-biased emissivity field predicted by ourprescriptions for star formation and feedback, which have previously been shownto account for a wide array of measurements of the post-reionization Universe.It is qualitatively robust to our choice of simulation volume, ionizing escapefraction, and spatial resolution in fact it grows stronger at higher spatialresolution even though the exact overlap redshift is sensitive to each ofthese. However, it weakens slightly as the escape fraction is increased owingto the reduced density contrast at higher redshift. We also explore whether ourresults are sensitive to commonly-employed approximations such as usingoptically-thin Eddington tensors or substantially altering the speed of light.Such approximations do not qualitatively change the topology of reionization.However, they can systematically shift the overlap redshift by up to $\Deltaz\sim 0.5$, indicating that accurate radiative transfer is essential forcomputing reionization. Our model cannot simultaneously reproduce the observedoptical depth to Thomson scattering and ionization rate per hydrogen atom at$z=6$, which could owe to numerical effects and-or missing early sources ofionization.



Author: K. Finlator, F. Ozel, R. Dave, B. D. Oppenheimer

Source: https://arxiv.org/



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