Probing the Global 21-cm Signal via the Integrated Sachs-Wolfe Effect on the 21-cm Background

TL;DR

This paper introduces a new method to study the global 21-cm background using the integrated Sachs-Wolfe effect, which helps mitigate foreground issues and allows for cross-verification of existing measurements.

Contribution

It proposes leveraging the 21-cm ISW effect as a novel probe of the global 21-cm signal evolution, offering a complementary approach to traditional methods.

Findings

Feasible with phase-1 SKA in a few thousand hours

Can cross-check EDGES and SARAS measurements

Mitigates Milky Way foreground challenges

Abstract

We propose a novel method to probe the global 21-cm background. This background experiences the integrated Sachs-Wolfe effect (ISW) as the cosmic microwave background does. The 21-cm ISW is modulated by the spectral shape of the global 21-cm signal, and thus the measure of the 21-cm ISW will be a probe of the evolution of the global signal. This strategy naturally mitigates the impact of the Milky Way foreground, which is a common and most significant challenge in conventional 21-cm background probes. With the phase-1 SKA telescope, probing the global 21-cm background would be feasible with a few 1000 hours of observation, enabling consistency checks with existing measures of the global 21-cm signal by EDGES and SARAS that are conflicting with each other.