Detectability and Model Discriminability of the Dark Ages 21 cm Global Signal

TL;DR

This paper evaluates the detectability and model discrimination of the Dark Ages 21 cm global signal using Bayesian methods, highlighting the importance of low-frequency observations and spectral shape in cosmological model testing.

Contribution

It provides a Bayesian framework to assess the detectability of the 21 cm signal and demonstrates the potential to distinguish cosmological models with limited frequency data.

Findings

Wide-band 1-50 MHz observations can detect non-zero 21 cm signals.

Observations below 15 MHz are crucial to break foreground degeneracies.

Even with 5 MHz interval measurements, the 21 cm spectral shape can be identified with low errors.

Abstract

The 21 cm signal from neutral hydrogen atom is almost the only way to directly probe the Dark Ages. The Dark Ages 21 cm signal, observed at frequencies below 50 MHz, can serve as a powerful probe of cosmology, as the standard cosmological model predicts a well-defined 21 cm spectral shape. In this work, we assess the detectability and model-selection power of 21 cm observations assuming physically motivated foregrounds, optimistic error levels, and several observing strategies for the signals predicted in various cosmological models. Using a Bayesian evidence-based comparison, we find that wide-band observations covering 1-50 MHz can identify the evidence of non-zero 21 cm signals from models considered in this paper except the one with a smooth spectrum that peaks at lower frequencies. In particular, observations below 15 MHz are essential to avoid degeneracies with the foreground. Furthermore, even with observations measured at 5 MHz intervals over the frequency range 1-50 MHz, the 21 cm signal can be identified if the errors are sufficiently small. This indicates that the intrinsic 21 cm spectral shape can be captured without foreground degeneracy even with a limited number of frequency channels.