Witnessing the onset of reionization through Lyman-α emission at redshift 13

Cosmic reionization began when ultraviolet (UV) radiation produced in the first galaxies began illuminating the cold, neutral gas that filled the primordial Universe<sup>1,2</sup>. Recent James Webb Space Telescope (JWST) observations have shown that surprisingly UV-bright galaxies were in place beyond redshift z = 14, when the Universe was less than 300 Myr old<sup>3-5</sup>. Smooth turnovers of their UV continua have been interpreted as damping-wing absorption of Lyman-α (Ly-α), the principal hydrogen transition<sup>6-9</sup>. However, spectral signatures encoding crucial properties of these sources, such as their emergent radiation field, largely remain elusive. Here we report spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES<sup>10</sup>) of a galaxy at redshift z = 13.0 that reveals a singular, bright emission line unambiguously identified as Ly-α, as well as a smooth turnover. We observe an equivalent width of EW<sub>Ly-α</sub> > 40 Å (rest frame), previously only seen at z < 9 where the intervening intergalactic medium becomes increasingly ionized<sup>11</sup>. Together with an extremely blue UV continuum, the unexpected Ly-α emission indicates that the galaxy is a prolific producer and leaker of ionizing photons. This suggests that massive, hot stars or an active galactic nucleus have created an early reionized region to prevent complete extinction of Ly-α, thus shedding new light on the nature of the earliest galaxies and the onset of reionization only 330 Myr after the Big Bang.

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Journal
Nature
Published
2025-03-26
DOI
https://doi.org/10.1038/s41586-025-08779-5
Citations
42
Primary Topic
Stellar, planetary, and galactic studies
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article
Field-Weighted Citation Impact
48.50
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article

Witnessing the onset of reionization through Lyman-α emission at redshift 13

Nimisha Kumari, Francesco D’Eugenio, Joris Witstok, Santiago Arribas et al.
42 citations
Nature
Stellar, planetary, and galactic studies
48.50
article

Witnessing the onset of reionization through Lyman-α emission at redshift 13

Nimisha Kumari, Francesco D’Eugenio, Joris Witstok, Santiago Arribas, Jakob M. Helton, Fengwu Sun, R. Maiolino, Benjamin D. Johnson, Stefano Carniani, Kevin Hainline, Jan Scholtz, Jacopo Chevallard, Sandro Tacchella, Alex J. Cameron, Chris J. Willott, Rachana Bhatawdekar, Gareth C. Jones, Pablo G. Pérez‐González, S. Charlot, Mirko Curti, Christina C. Williams, Yongda Zhu, Aayush Saxena, Pierluigi Rinaldi, Daniel J. Eisenstein, Hannah Übler, Stacey Alberts, P. Jakobsen, Emma Curtis-Lake, Christopher N. A. Willmer, William Baker, Kristan Boyett, Andrew J. Bunker, Phillip A. Cargile, Brant E. Robertson, Michael V. Maseda, Renske Smit
article en
42 citations

Abstract

Cosmic reionization began when ultraviolet (UV) radiation produced in the first galaxies began illuminating the cold, neutral gas that filled the primordial Universe<sup>1,2</sup>. Recent James Webb Space Telescope (JWST) observations have shown that surprisingly UV-bright galaxies were in place beyond redshift z = 14, when the Universe was less than 300 Myr old<sup>3-5</sup>. Smooth turnovers of their UV continua have been interpreted as damping-wing absorption of Lyman-α (Ly-α), the principal hydrogen transition<sup>6-9</sup>. However, spectral signatures encoding crucial properties of these sources, such as their emergent radiation field, largely remain elusive. Here we report spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES<sup>10</sup>) of a galaxy at redshift z = 13.0 that reveals a singular, bright emission line unambiguously identified as Ly-α, as well as a smooth turnover. We observe an equivalent width of EW<sub>Ly-α</sub> > 40 Å (rest frame), previously only seen at z < 9 where the intervening intergalactic medium becomes increasingly ionized<sup>11</sup>. Together with an extremely blue UV continuum, the unexpected Ly-α emission indicates that the galaxy is a prolific producer and leaker of ionizing photons. This suggests that massive, hot stars or an active galactic nucleus have created an early reionized region to prevent complete extinction of Ly-α, thus shedding new light on the nature of the earliest galaxies and the onset of reionization only 330 Myr after the Big Bang.

NatureVol. 639(8056)
Herzberg Institute of Astrophysics (CA), University of Copenhagen (DK), Centre National de la Recherche Scientifique (FR), Space Telescope Science Institute (US), European Southern Observatory (DE), University of Wisconsin–Madison (US), University of Arizona (US), University of Hertfordshire (GB), Scuola Normale Superiore (IT), University of California, Santa Cruz (US), University of Cambridge (GB), Institut d'Astrophysique de Paris (FR), Brera Astronomical Observatory (IT), Sorbonne Université (FR), University of Oxford (GB), Max Planck Institute for Extraterrestrial Physics (DE), European Space Astronomy Centre (ES), DAWN Center for Independent Living (US), Center for Astrophysics Harvard & Smithsonian (US), Centro de Astrobiología (ES), NSF NOIRLab (US), University College London (GB), Liverpool John Moores University (GB), IT University of Copenhagen (DK)
Openalex Percentile: Top 0%
Stellar, planetary, and galactic studies
48.50
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