TITLE:
Primordial helium recombination I: feedback, line transfer, and continuum opacity.
AUTHOR(S):
Eric R. Switzer (Princeton); Christopher M. Hirata (IAS).
DATE:
2007 Feb 06 (arXiv, posted, v1);
2007 Mar 11 (Phys. Rev. D, submitted);
2008 Feb 12 (revised);
2008 Feb 24 (Phys. Rev. D, accepted);
2008 Apr 30 (Phys. Rev. D, published).
AVAILABILITY:
arXiv astro-ph/0702143 (free);
APS (requires subscription).
PUBLICATION INFORMATION:
Phys. Rev. D 77, 083006 (2008).
ABSTRACT:
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 HeI lines with partial redistribution, and continuum opacity from HI
photoionization. In agreement with past calculations, we find that HeII recombination proceeds in Saha equilibrium, whereas HeI recombination is
delayed relative to Saha due to the low rates connecting excited states of HeI to the ground state. However, we find that at z<2200 the continuum
absorption by the rapidly increasing HI population becomes effective at destroying photons in the HeI 21Po-11S line,
causing HeI recombination to finish around z~1800, much earlier than previously estimated.
ADS BIBLIOGRAPHIC CODE:
2008PhRvD..77h3006S
COMMENTS:
This is the first in a series of three papers on helium recombination; see Paper II and Paper
III.