Concerns about Modelling of the EDGES Data

TL;DR

This paper critically examines the modelling of the EDGES data, questioning the physical plausibility and uniqueness of the claimed 21-cm absorption detection, and highlights potential issues in the interpretation of the results.

Contribution

It reveals that the modelling process used for EDGES data may produce unphysical parameters and non-unique solutions, challenging the original interpretation of the 21-cm signal detection.

Findings

The EDGES data modelling implies unphysical foreground parameters.

Multiple simple models can fit the data with different shapes.

The original detection claim may not be unambiguous.

Abstract

It is predicted that the spectrum of radio emission from the whole sky should show a dip arising from the action of the light from the first stars on the hydrogen atoms in the surrounding gas, which causes the 21-cm line to appear in absorption against the cosmic microwave background. Bowman et al. 2018 identified a broad flat-bottomed absorption profile centred at 78 MHz, which could be this feature, although the depth of the profile is much larger than expected. We have examined the modelling process they used and find that their data implies unphysical parameters for the foreground emission and also that their solution is not unique in the sense that we found other simple formulations for the signal that are different in shape but that also fit their data. We argue that this calls into question the interpretation of these data as an unambiguous detection of the cosmological 21-cm absorption signature.