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Primordial helium recombination. I. Feedback, line transfer, and continuum opacity

Switzer, Eric R. and Hirata, Christopher M. (2008) Primordial helium recombination. I. Feedback, line transfer, and continuum opacity. Physical Review D, 77 (8). Art. No. 083006. ISSN 0556-2821.

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Precision measurements of the cosmic microwave background temperature anisotropy on scales ℓ>500 will be available in the near future. Successful interpretation of these data is dependent on a detailed understanding of the damping tail and cosmological recombination of both hydrogen and helium. This paper and two companion papers are devoted to a precise calculation of helium recombination. We discuss several aspects of the standard recombination picture, and then include feedback, radiative transfer in He i lines with partial redistribution, and continuum opacity from H i photoionization. In agreement with past calculations, we find that He ii recombination proceeds in Saha equilibrium, whereas He i recombination is delayed relative to Saha due to the low rates connecting excited states of He i to the ground state. However, we find that at z<2200 the continuum absorption by the rapidly increasing H i population becomes effective at destroying photons in the He i 21Po-11S line, causing He i recombination to finish around z≃1800, much earlier than previously estimated.

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Additional Information:©2008 The American Physical Society. (Received 10 March 2007; published 30 April 2008) E.S. acknowledges the support from grants from NASA No. LTSAA03-000-0090 and NSF No. PHY-0355328. We acknowledge useful conversations with Jens Chluba, Bruce Draine, Jim Peebles, Doug Scott, Uroš Seljak, and Rashid Sunyaev. We also thank Joanna Dunkley for critical readings and comments prior to publication.
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National Science FoundationPHY-0355328
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11097
Deposited By: Archive Administrator
Deposited On:15 Jul 2008 00:05
Last Modified:26 Dec 2012 10:09

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