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. http://resolver.caltech.edu/CaltechAUTHORS:SWIprd08
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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.
|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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|Deposited On:||15 Jul 2008 00:05|
|Last Modified:||26 Dec 2012 10:09|
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