Understanding the Diversity of 21 cm Cosmology Analyses

TL;DR

This paper classifies diverse 21 cm cosmology analysis methods into two main families based on their statistical approach, clarifying their differences in sensitivity to foregrounds and calibration errors, and guiding future analysis strategies.

Contribution

It introduces a unifying classification of 21 cm analysis techniques into two families, explaining their distinct susceptibilities and implications for cosmological research.

Findings

All existing methods fall into two categories based on the statistical question they pose.

The two families differ in their sensitivity to foreground contamination.

Understanding these differences can improve analysis robustness and interpretation.

Abstract

21 cm power spectrum observations have the potential to revolutionize our understanding of the Epoch of Reionization and Dark Energy, but require extraordinarily precise data analysis methods to separate the cosmological signal from the astrophysical and instrumental contaminants. This analysis challenge has led to a diversity of proposed analyses, including delay spectra, imaging power spectra, m-mode analysis, and numerous others. This diversity of approach is a strength, but has also led to confusion within the community about whether insights gleaned by one group are applicable to teams working in different analysis frameworks. In this paper we show that all existing analysis proposals can be classified into two distinct families based on whether they estimate the power spectrum of the measured or reconstructed sky. This subtle difference in the statistical question posed largely determines the susceptibility of the analyses to foreground emission and calibration errors, and ultimately the science different analyses can pursue. In this paper we detail the origin of the two analysis families, categorize the analyses being actively developed, and explore their relative sensitivities to foreground contamination and calibration errors.