The REACH radiometer for detecting the 21-cm hydrogen signal from redshift 7.5 to 28

TL;DR

The REACH radiometer aims to detect the 21-cm hydrogen signal from early universe epochs with improved systematic handling, using innovative dual-antenna observations and Bayesian analysis to better understand cosmic dawn and reionization.

Contribution

REACH introduces a novel experimental approach with simultaneous dual-antenna observations and Bayesian analysis to address systematic issues in 21-cm cosmology measurements.

Findings

Forecasts percent-level constraints on astrophysical parameters

Demonstrates improved systematic mitigation techniques

Potential to confirm or refute the EDGES absorption feature

Abstract

Observations of the 21-cm line from primordial hydrogen promise to be one of the best tools to study the early epochs of the Universe: the Dark Ages, the Cosmic Dawn, and the subsequent Epoch of Reionization. In 2018, the EDGES experiment caught the attention of the cosmology community with a potential detection of an absorption feature in the sky-averaged radio spectrum centred at 78 MHz. The feature is deeper than expected, and, if confirmed, would call for new physics. However, different groups have re-analyzed the EDGES data and questioned the reliability of the signal. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a sky-averaged 21-cm experiment aiming at improving the current observations by tackling the issues faced by current instruments related to residual systematic signals in the data. The novel experimental approach focuses on detecting and jointly explaining these systematics together with the foregrounds and the cosmological signal using Bayesian statistics. To achieve this, REACH features simultaneous observations with two different antennas, an ultra wideband system (redshift range 7.5 to 28), and a receiver calibrator based on in-field measurements. Simulated observations forecast percent-level constraints on astrophysical parameters, potentially opening up a new window to the infant Universe.