The Redshifted 21 cm Signal in the EDGES Low-band Spectrum
Bibliographic record
Abstract
The EDGES collaboration reported an unexpectedly deep absorption in the radio background at 78 MHz and interpreted the dip as the first detection of a redshifted 21 cm signal from cosmic dawn (CD). We attempt an alternate analysis by 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 ± 35 mK. The depth of the 21 cm absorption inferred by the EDGES analysis required invoking nonstandard cosmology, or new physics, or new sources at CD, 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 there exists a residual unmodeled systematic sinusoidal feature, and we explore this possibility further by examining for additional 21 cm signal. The data then favor an absorption with Gaussian model parameters of amplitude 133 ± 60 mK, best width at half-power 9 ± 3 MHz, and center frequency 72.5 ± 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. 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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".