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Lyman-alpha transfer in primordial hydrogen recombination

Hirata, Christopher M. and Forbes, John (2009) Lyman-alpha transfer in primordial hydrogen recombination. Physical Review D, 80 (2). 023001. ISSN 1550-7998.

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Cosmological constraints from the cosmic microwave background (CMB) anisotropies rely on accurate theoretical calculations of the cosmic recombination history. Recent work has emphasized the importance of radiative transfer calculations due to the high optical depth in the H i Lyman lines. Transfer in the Lyalpha line is dominated by true emission and absorption, Hubble expansion, and resonant scattering. Resonant scattering causes photons to diffuse in frequency due to random kicks from the thermal velocities of hydrogen atoms, and also to drift toward lower frequencies due to energy loss via atomic recoil. Past analyses of Lyalpha transfer during the recombination era have either considered a subset of these processes, ignored time dependence, or incorrectly assumed identical emission and absorption profiles. We present here a fully time-dependent radiative transfer calculation of the Lyalpha line including all of these processes, and compare it to previous results that ignored the resonant scattering. We find a faster recombination due to recoil enhancement of the Lyalpha escape rate, leading to a reduction in the free electron density of 0.45% at z=900. This results in an increase in the small-scale CMB power spectrum that is negligible for the current data but will be a 0.9sigma correction for Planck. We discuss the reasons why we find a smaller correction than some other recent computations.

Item Type:Article
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Hirata, Christopher M.0000-0002-2951-4932
Additional Information:©2009 The American Physical Society. Received 3 April 2009; revised 18 June 2009; published 6 July 2009. We thank Y. Ali-Haïmoud, D. Grin, and E. Switzer for useful discussions and comments. This project was supported by the U.S. Department of Energy (DE-FG03-92-ER40701) and the National Science Foundation (AST-0807337). C. H. is supported by the Alfred P. Sloan Foundation. J. F. received support from Caltech and the Flintridge Foundation. 98.70.Vc Cosmic background radiations 32.80.Rm Multiphoton ionization and excitation to highly excited states in atoms 98.62.Ra Intergalactic matter; quasar absorption and emission-line systems; Lyman forest
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-92-ER40701
Alfred P. Sloan FoundationUNSPECIFIED
Flintridge FoundationUNSPECIFIED
Subject Keywords:PACS: 98.70.Vc; 32.80.Rm; 98.62.Ra
Issue or Number:2
Record Number:CaltechAUTHORS:20090817-144812847
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Official Citation:Lyman-alpha transfer in primordial hydrogen recombination Christopher M. Hirata and John Forbes, Phys. Rev. D 80, 023001 (2009), DOI:10.1103/PhysRevD.80.023001
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15087
Deposited By: George Porter
Deposited On:08 Sep 2009 20:49
Last Modified:03 Oct 2019 00:54

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