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A lower limit of Δz > 0.06 for the duration of the reionization epoch

Abstract

Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies1. The observations are challenging, though, because of the low expected signal strength (10 mK), and contamination by strong (>100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature2,3,4 visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 < z < 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of Δz < 0.06 at the 95% confidence level.

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Figure 1: Measured spectrum between 100 and 195 MHz.
Figure 2: Lower confidence bounds on the duration of the reionization transition. Statistical and systematic uncertainties are included.

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Acknowledgements

This work was supported by the NSF. J.D.B was supported during part of this work at the California Institute of Technology by NASA through a Hubble Fellowship awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy for NASA. This scientific work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. We thank CSIRO and Curtin University for logistical support and D. DeBoer, D. Herne, D. Emrich, M. Halleen and C. Halleen for on-site support.

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Both authors contributed equally to the work in this paper.

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Correspondence to Judd D. Bowman.

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Supplementary Information

This file contains Supplementary Information comprising Description of the EDGES radio spectrometer, Analog-to-Digital Conversion, Compact, Planar, Dual-Octave Antenna and Ground Screen, Calibration and Data Interpretation, Selection of Observing Site, Supplementary Figures 1-2 with legends and additional references. (PDF 1108 kb)

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Bowman, J., Rogers, A. A lower limit of Δz > 0.06 for the duration of the reionization epoch. Nature 468, 796–798 (2010). https://doi.org/10.1038/nature09601

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