Models of polarized Lyman-alpha emission from cosmic ionization fronts and extraction of front parameters from 21cmFAST tool

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2022-05

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The Ohio State University

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Abstract

The epoch of reionization is one main history of the universe, and it gives both cosmologists and astrophysicists insights into energy radiation, cosmic microwave background (CMB), galaxy formation, etc. Intensity mapping (IM) is one of the novel methods in probing the reionization, and Lyman-α forest is one of its main focuses. Thus, I want to study the epoch of reionization by looking at the Lyman-α emission from that period. In this paper, I present the formalism of simulating Lyman-α emission and polarization from a signal plane-parallel ionization front at redshift z = 8 and show the method of extracting needed parameters from the 21cmFAST tool. To build the model, I first use the Lyman-α emissivity to generate a Lyman-α photon from a presetting ionization front. Then I propagate the Lyman-α photon at a distance related to its mean free path and hit it with a hydrogen atom. The Lyman-α photon will scatter and repeat those steps until it hits either the boundary of the front of the frequency limit. After the Lyman-α photon hits the limits and escapes, I record its basic information, such as escaping position, direction, polarization, and frequency, for further calculation, such as the intensity, polarized intensity, and power spectrum of the front. The parameters for this model are blackbody temperature Tbb, front velocity U, and number density of neutral hydrogen nH. To expand this model into coeval cubes, the model that contains all the information of the universe under a fixed time, generated by the 21cmFAST tool, as Tbb is set, I will calculate U and nH from the coeval data boxes. The source code can be found at https://github.com/SourceYang/Lyman-alpha

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Astrophysics, Reionization, Lyman-alpha emission, Monte Carlo, Polarization

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