Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sightlines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day1,2. Observations of the cosmic microwave background3, and of galaxies and quasars at the highest redshifts4, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z ≈ 6. Detecting ionizing Lyman-α photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Lyα photons emitted less than 600 million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549 ± 0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 8). We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby9.
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We thank the Director General of the ESO for generous allocation of time and the staff on Paranal for conducting the observations. We also thank F. Combes, S. Zaroubi, M. Haehnelt, D. Valls-Gabaud and J. Dunlop for discussions.
The authors declare no competing financial interests.
This file contains Supplementary Information comprising: Observations and data reduction; The nature of the line and Other Possible Sources of Line Emission. It also contains Supplementary Figures 1-3 with legends and additional references. (PDF 168 kb)
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Lehnert, M., Nesvadba, N., Cuby, JG. et al. Spectroscopic confirmation of a galaxy at redshift z = 8.6. Nature 467, 940–942 (2010). https://doi.org/10.1038/nature09462
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