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Concerns about modelling of the EDGES data

Nature volume 564, pages E32–E34 (2018)Cite this article

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arising from J. D. Bowman, A. E. E. Rogers, R. A. Monsalve, T. J. Mozdzen & N. Mahesh Nature 555, 67–70 (2018); https://doi.org/10.1038/nature25792

It is predicted1 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.2 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. There is a Reply to this Comment by Bowman, J. D. et al. Nature 564, https://doi.org/10.1038/s41586-018-0797-4 (2018).

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Fig. 1: Fits to the EDGES data.
Fig. 2: Further illustrations of the fitting process.

Data availability

For all our analyses we used the ‘Data for Figure 1 of Bowman et al. (2018)’ in the EDGES Data Release, which is available at http://loco.lab.asu.edu/edges/edges-data-release/.

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Author information

Author notes

  1. Girish Kulkarni

    Present address: Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai, India

  2. Ewald Puchwein

    Present address: Leibniz Institute for Astrophysics, Potsdam, Germany

Authors and Affiliations

  1. Cavendish Laboratory, University of Cambridge, Cambridge, UK

    Richard Hills

  2. Institute of Astronomy, University of Cambridge, Cambridge, UK

    Girish Kulkarni, P. Daniel Meerburg & Ewald Puchwein

  3. Kavli Institute for Cosmology, University of Cambridge, Cambridge, UK

    Girish Kulkarni, P. Daniel Meerburg & Ewald Puchwein

  4. Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK

    P. Daniel Meerburg

  5. Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands

    P. Daniel Meerburg

  6. Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Groningen, The Netherlands

    P. Daniel Meerburg

Authors
  1. Richard Hills
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  2. Girish Kulkarni
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  4. Ewald Puchwein
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Contributions

E.P. initiated this study by pointing out the importance of the role of the foreground parameters in the claimed detection of an absorption profile. All authors participated in the detailed analysis and the writing of the Comment.

Corresponding author

Correspondence to Richard Hills.

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Competing interests

Declared none.

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Supplementary Information

This file contains Supplementary Information including Supplementary Figures 1 to 11 and Supplementary Tables 1 and 2.

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Hills, R., Kulkarni, G., Meerburg, P.D. et al. Concerns about modelling of the EDGES data. Nature 564, E32–E34 (2018). https://doi.org/10.1038/s41586-018-0796-5

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