# The redshifted 21-cm signal in the EDGES low-band spectrum

## TL;DR

This paper reanalyzes the EDGES low-band spectrum for the redshifted 21-cm signal, suggesting the observed absorption could be consistent with standard cosmology when modeled with alternative foreground and systematic assumptions.

## Contribution

It introduces a maximally smooth function approach for foreground modeling and explores residual systematic features, challenging previous claims of non-standard physics.

## Key findings

- Best-fit absorption amplitude of 921 ± 35 mK with smooth foreground modeling
- Alternative Gaussian fit suggests a shallower absorption of 133 ± 60 mK
- Spectrum is compatible with some standard 21-cm models without new physics

## Abstract

The EDGES collaboration reported the finding of an unexpectedly deep absorption in the radio background at 78 MHz and interpreted the dip as a first detection of redshifted 21-cm from Cosmic Dawn. We have attempted an alternate analysis, adopting a maximally smooth function approach to model the foreground. A joint fit to the spectrum using such a function together with a flattened absorption profile yields a best fit absorption amplitude of $921 \pm 35$ mK. The depth of the 21-cm absorption inferred by the EDGES analysis required invoking non-standard cosmology or new physics or new sources at Cosmic Dawn and this tension with accepted models is compounded by our analysis that suggests absorption of greater depth. Alternatively, the measured spectrum may be equally-well fit assuming that there exists a residual unmodeled systematic sinusoidal feature and we explore this possibility further by examining for any additional 21-cm signal. The data then favors an absorption with Gaussian model parameters of amplitude $133 \pm 60$ mK, best width at half-power $9 \pm 3$ MHz and center frequency $72.5 \pm 0.8$ MHz. We also examine the consistency of the measured spectrum with plausible redshifted 21-cm models: a set of 3 of the 265 profiles in the global 21-cm atlas of Cohen et al. 2017 are favored by the spectrum. We conclude that the EDGES data may be consistent with standard cosmology and astrophysics, without invoking excess radio backgrounds or baryon-dark matter interactions.