HeII->HeI Recombination of Primordial Helium Plasma Including the Effect of Neutral Hydrogen

TL;DR

This paper studies the HeII to HeI recombination in primordial helium plasma, emphasizing the importance of photon redistribution effects and neutral hydrogen influence on cosmic microwave background features.

Contribution

It introduces a detailed analysis of resonance photon redistribution effects on HeII to HeI recombination kinetics, highlighting the significance of including these effects in cosmological models.

Findings

Redistribution effects cause 1-3.8% differences in free electron counts.

Proper modeling requires considering both wings of resonance lines and photon redistribution.

Neutral hydrogen impacts the recombination process during z = 1500 - 3000.

Abstract

The HeII->HeI recombination of primordial helium plasma (z = 1500 - 3000) is considered in terms of the standard cosmological model. This process affects the formation of cosmic microwave background anisotropy and spectral distortions. We investigate the effect of neutral hydrogen on the HeII->HeI recombination kinetics with partial and complete redistributions of radiation in frequency in the HeI resonance lines. It is shown that to properly compute the HeII->HeI recombination kinetics, one should take into account not only the wings in the absorption and emission profiles of the HeI resonance lines, but also the mechanism of the redistribution of resonance photons in frequency. Thus, for example, the relative difference in the numbers of free electrons for the model using Doppler absorption and emission profiles and the model using a partial redistribution in frequency is 1 - 1.3% for the epoch z = 1770 - 1920. The relative difference in the numbers of free electrons for the model using a partial redistribution in frequency and the model using a complete redistribution in frequency is 1 - 3.8% for the epoch z = 1750 - 2350.