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Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal


Observations of the redshifted 21-cm line of atomic hydrogen have provided several upper limits on the 21-cm power spectrum and a tentative detection of the sky-averaged signal at redshift z ≈ 17. Made with the Experiment to Detect the Global EoR Signature (EDGES) low-band antenna, this claim was recently disputed by the SARAS 3 experiment, which reported a non-detection and is the only available upper limit strong enough to constrain cosmic dawn astrophysics. We use these data to constrain a population of radio-luminous galaxies ~200 million years after the Big Bang (z ≈ 20). We find, using Bayesian data analysis, that the data disfavour (at 68% confidence) radio-luminous galaxies in dark-matter haloes with masses of 4.4 × 105MM 1.1 × 107M (where M is the mass of the Sun) at z = 20 and galaxies in which >5% of the gas is converted into stars. The data disfavour galaxies with a radio luminosity per star formation rate of Lr/SFR  1.549 × 1025 W Hz−1M−1 yr at 150 MHz, around 1,000 times brighter than today, and, separately, a synchrotron radio background in excess of the cosmic microwave background by 6% at 1.42 GHz.

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Fig. 1: SARAS 3 constraints on high-redshift radio galaxies.
Fig. 2: The relationship between the astrophysical parameters and the noise.
Fig. 3: The relationship between the foreground and astrophysical parameters.

Data availability

The SARAS 3 data are available upon reasonable request from S.S. (

Code availability

GLOBALEMU is available at and MARGARINE at The nested sampling tool POLYCHORD is available at and the nested sampling post-processing codes ANESTHETIC and FGIVENX are available at and, respectively. All other codes used are available upon reasonable request from the corresponding author.


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H.T.J.B. acknowledges the support of the Science and Technology Facilities Council (STFC) through grant number ST/T505997/1. W.J.H. and A.F. were supported by Royal Society University Research Fellowships. E.d.L.A. was supported by the STFC through the Ernest Rutherford Fellowship. R.B. acknowledges the support of the Israel Science Foundation (grant number 2359/20), The Ambrose Monell Foundation and the Institute for Advanced Study, as well as the Vera Rubin Presidential Chair in Astronomy and the Packard Foundation.

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H.T.J.B. performed the data analysis and led the writing of the paper. A.F. initiated the project, supervised it and helped write and revise the article. E.d.L.A. supervised the project and the analysis and helped write and revise the article. W.J.H. provided technical support and advice regarding the Bayesian methodology. R.S. and S.S. provided the non-public data used in the analysis. The astrophysical signal models were provided by A.F. and R.B. All authors provided comments and contributed to the structure of the article.

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Correspondence to H. T. J. Bevins.

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Bevins, H.T.J., Fialkov, A., de Lera Acedo, E. et al. Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal. Nat Astron 6, 1473–1483 (2022).

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