Background reionization history from omniscopes

TL;DR

This paper investigates how background reionization history affects cosmological parameter estimation from 21-cm observations, emphasizing the importance of degeneracy control and combining multiple data sources for accurate constraints.

Contribution

It introduces a Markov Chain Monte Carlo approach on simulated 21-cm data to analyze degeneracies and proposes combining CMB data with multi-redshift observations for improved reionization parameter estimation.

Findings

Fisher matrix analysis aligns with MCMC when degeneracies are controlled.

Combining CMB and multi-redshift data improves reionization parameter constraints.

Unresolved ionizing sources significantly degrade reionization parameter estimates.

Abstract

The measurements of the 21-cm brightness temperature fluctuations from the neutral hydrogen at the Epoch of Reionization (EoR) should inaugurate the next generation of cosmological observables. In this respect, many works have concentrated on the disambiguation of the cosmological signals from the dominant reionization foregrounds. However, even after perfect foregrounds removal, our ignorance on the background reionization history can significantly affect the cosmological parameter estimation. In particular, the interdependence between the hydrogen ionized fraction, the baryon density and the optical depth to the redshift of observation induce nontrivial degeneracies between the cosmological parameters that have not been considered so far. Using a simple, but consistent reionization model, we revisit their expected constraints for a futuristic giant 21-cm omniscope by using for the first time Markov Chain Monte Carlo (MCMC) methods on multiredshift full sky simulated data. Our results agree well with the usual Fisher matrix analysis on the three-dimensional flat sky power spectrum but only when the above-mentioned degeneracies are kept under control. In the opposite situation, Fisher results can be inaccurate. We show that these conditions can be fulfilled by combining cosmic microwave background measurements with multiple observation redshifts probing the beginning of EoR. This allows a precise reconstruction of the total optical depth, reionization duration and maximal spin temperature. Finally, we discuss the robustness of these results in presence of unresolved ionizing sources. Although most of the standard cosmological parameters remain weakly affected, we find a significant degradation of the background reionization parameter estimation in presence of nuisance ionizing sources.