Mapmaking for Precision 21 cm Cosmology

TL;DR

This paper develops methods to accurately and efficiently create sky maps from interferometric data for 21 cm cosmology, enabling better separation of the cosmological signal from foregrounds during the Epoch of Reionization.

Contribution

It introduces approximate yet rigorous techniques for mapmaking that account for interferometer effects, improving sensitivity and computational efficiency for 21 cm cosmology experiments.

Findings

Methods increase sensitivity to the 21 cm signal.

Approximations significantly reduce computational costs.

Case study demonstrates practical utility for HERA.

Abstract

In order to study the "Cosmic Dawn" and the Epoch of Reionization with 21 cm tomography, we need to statistically separate the cosmological signal from foregrounds known to be orders of magnitude brighter. Over the last few years, we have learned much about the role our telescopes play in creating a putatively foreground-free region called the "EoR window." In this work, we examine how an interferometer's effects can be taken into account in a way that allows for the rigorous estimation of 21 cm power spectra from interferometric maps while mitigating foreground contamination and thus increasing sensitivity. This requires a precise understanding of the statistical relationship between the maps we make and the underlying true sky. While some of these calculations would be computationally infeasible if performed exactly, we explore several well-controlled approximations that make mapmaking and the calculation of map statistics much faster, especially for compact and highly redundant interferometers designed specifically for 21 cm cosmology. We demonstrate the utility of these methods and the parametrized trade-offs between accuracy and speed using one such telescope, the upcoming Hydrogen Epoch of Reionization Array, as a case study.