Will Nonlinear Peculiar Velocity and Inhomogeneous Reionization Spoil 21cm Cosmology from the Epoch of Reionization?

TL;DR

This paper investigates how nonlinear effects from peculiar velocities and inhomogeneous reionization impact the ability to extract cosmological information from 21cm observations during the epoch of reionization, using detailed simulations.

Contribution

It provides the first detailed test of the separation scheme's validity in 21cm cosmology considering nonlinear fluctuations.

Findings

Separation scheme works well early in reionization (<40% ionized)

Scheme breaks down at late stages (>80% ionized)

Nonlinear effects significantly affect 21cm cosmological measurements

Abstract

The 21cm background from the epoch of reionization is a promising cosmological probe: line-of-sight velocity fluctuations distort redshift, so brightness fluctuations in Fourier space depend upon angle, which linear theory shows can separate cosmological from astrophysical information. Nonlinear fluctuations in ionization, density and velocity change this, however. The validity and accuracy of the separation scheme are tested here for the first time, by detailed reionization simulations. The scheme works reasonably well early in reionization (< 40% ionized), but not late (> 80% ionized).