Primordial helium recombination I: feedback, line transfer, and continuum opacity

Abstract

Precision measurements of the cosmic microwave background temperature anisotropy on scales $\ell >500$ 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 $2^1{P}^o-1^{1}S$ line, causing HeI recombination to finish around $z\approx 1800$, much earlier than previously estimated.

30 pages, 13 figures, to be submitted to PRD

References in corpus (3)

• The effect of forbidden transitions on cosmological hydrogen and helium recombination
• Two-Photon 2s<->1s Transitions during Recombination of Hydrogen in the Universe
• Linear effects of perturbed recombination

Cited by in corpus (6)

• Two-photon transitions in primordial hydrogen recombination
• Probing the Effective Number of Neutrino Species with Cosmic Microwave Background
• Primordial helium recombination III: Thomson scattering, isotope shifts, and cumulative results
• Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast
• WMAP 5-year constraints on time variation of $\alpha$ and $m_e$ in a detailed recombination scenario
• Delayed Recombination and Cosmic Parameters