Linear effects of perturbed recombination

TL;DR

This paper investigates how small perturbations in the ionization fraction after recombination influence the evolution of gas temperature and baryon perturbations, affecting 21cm signals and structure formation.

Contribution

It provides a linear analysis of the effects of ionization fraction perturbations on gas temperature and baryon perturbations during the post-recombination era.

Findings

Perturbations significantly influence gas temperature evolution on all scales.

Galactic-scale baryon perturbations are altered at the percent level at high redshifts.

Effects are relevant for understanding 21cm cosmology and early structure formation.

Abstract

Perturbations in the ionization fraction after recombination affect the Compton cooling of density perturbations. Once the gas temperature starts to decouple from the CMB temperature, ionization fraction perturbations can have a significant influence on the subsequent gas temperature perturbation evolution. This directly affects the 21cm spin temperature of the gas, and also modifies the small-scale baryon perturbation evolution via the difference in baryon pressure. The effect on the gas temperature perturbations can be significant on all scales, and galactic-scale baryon perturbations are modified at the percent level at redshifts z >~ 100 where numerical simulations are typically started.