2007/02/06 by Eric R. Switzer, Christopher M. Hirata
Chemistry · Physics and Astronomy · #Anisotropy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Cosmic microwave background #Cosmology and Gravitation Theories #Excited state #Galaxies: Formation, Evolution, Phenomena #Helium #Ion #Ionization #Opacity #Photoionization #Photon #Physics #Quantum mechanics #Radiative transfer #Recombination #Redistribution (election) #astro-ph
paper · pdf · doi:10.1103/physrevd.77.083006
published as Phys.Rev.D77:083006,2008 · 30 pages, 13 figures, to be submitted to PRD
arxiv created 2007/02/06 · openalex publication_date 2008/04/30 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Precision measurements of the cosmic microwave background temperature anisotropy on scales \ensuremathℓ>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\ensuremath-11S line, causing He i recombination to finish around z\ensuremath≈1800, much earlier than previously estimated.