Kavli Affiliate: Tom Abel
| First 5 Authors: Karsten Jedamzik, Tom Abel, Yacine Ali-Haimoud, ,
| Summary:
Primordial magnetic fields (PMFs) may explain observations of magnetic fields
on extragalactic scales. They are most cleanly constrained by measurements of
cosmic microwave background radiation (CMB) anisotropies. Their effects on
cosmic recombination may even be at the heart of the resolution of the Hubble
tension. We present the most detailed analysis of the effects of PMFs on cosmic
recombination to date. To this end we extend the public magneto-hydrodynamic
code {sl ENZO} with a new cosmic recombination routine, Monte-Carlo
simulations of Lyman-$alpha$ photon transport, and a Compton drag term in the
baryon momentum equation. The resulting code allows us, for the first time, to
realistically predict the impact of PMFs on the cosmic ionization history and
the clumping of baryons during cosmic recombination. Our results identify the
importance of mixing of Lyman-$alpha$ photons between overdense- and
underdense- regions for small PMF strength. This mixing speeds up recombination
beyond the speed-up due to clumping. We also investigate the effects of
pecuilar flows on the recombination rate and find it to be small for small PMF
strengths. For non-helical PMFs with a Batchelor spectrum we find a surprising
dependency of results on ultra-violet magnetic modes. We further show that the
increase in the ionization fraction at low redshift by hydrodynamic baryon
heating due to PMF dissipation is completely compensated by the faster
recombination from baryon clumping. The present study shall serve as a
theoretical foundation for a future precise comparison of recombination with
PMFs to CMB data.
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