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 Universe1,2. 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 old3-5. Smooth turnovers of their UV continua have been interpreted as damping-wing absorption of Lyman-α (Ly-α), the principal hydrogen transition6-9. 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 (JADES10) 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 EWLy-α > 40 Å (rest frame), previously only seen at z < 9 where the intervening intergalactic medium becomes increasingly ionized11. 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.

Description

Acknowledgements: We thank L. Keating, H. Katz, C. Witten, W. McClymont, A. van der Wel, J. Chisholm, D. Berg and M. Ouchi for useful discussions. This work is based on observations made with the National Aeronautics and Space Administration (NASA)/European Space Agency (ESA)/Canadian Space Agency (CSA) JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for the JWST. These observations are associated with programmes 1180, 1210, 1286, 1287 and 3215. J.W., R.M., W.M.B., F.D. and J.S. acknowledge support from the Science and Technology Facilities Council (STFC), by the European Research Council (ERC) through Advanced Grant 695671 ‘QUENCH’ and by the UK Research and Innovation (UKRI) Frontier Research grant RISEandFALL. J.W. also gratefully acknowledges support from the Cosmic Dawn Center through the DAWN Fellowship. The Cosmic Dawn Center is financed by the Danish National Research Foundation under grant no. 140. B.D.J., B.E.R., F.S., P.A.C., D.J.E., C.N.A.W. and Y.Z. acknowledge support from the JWST/NIRCam contract to the University of Arizona, NAS5-02015. B.E.R. also acknowledges support from JWST Program 3215. S.T. acknowledges support from Royal Society Research Grant G125142. A.J.C., A.J.B., A.S., J.C. and G.C.J. acknowledge support from the ‘FirstGalaxies’ Advanced Grant from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 789056). R.S. acknowledges support from a STFC Ernest Rutherford Fellowship (ST/S004831/1). S. Alberts acknowledges support from the JWST MIRI Science Team Lead, grant 80NSSC18K0555 and from NASA Goddard Space Flight Center to the University of Arizona. S. Arribas acknowledges grant PID2021-127718NB-I00 financed by the Spanish Ministry of Science and Innovation/State Agency of Research (MICIN/AEI/10.13039/501100011033). This research is supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. S. Carniani acknowledges support by the European Union’s HE ERC Starting Grant No. 101040227 ‘WINGS’. E.C.-L. acknowledges the support of an STFC Webb Fellowship (ST/W001438/1). D.J.E. is supported as a Simons Investigator. P.G.P.-G. acknowledges support from grant PID2022-139567NB-I00 financed by Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033, FEDER, UE. H.Ü. gratefully acknowledges support by the Isaac Newton Trust and by the Kavli Foundation through a Newton-Kavli Junior Fellowship. H.Ü. also acknowledges funding by the European Union (ERC APEX, 101164796). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. The research of C.C.W. is supported by NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. This study made use of the Prospero high-performance computing facility at Liverpool John Moores University.

Keywords

5101 Astronomical Sciences, 51 Physical Sciences

Journal Title

Nature

Journal ISSN

0028-0836
1476-4687

Volume Title

639

Publisher

Springer Nature

Publisher DOI

https://doi.org/10.1038/s41586-025-08779-5

Rights and licensing

Except where otherwised noted, this item's license is described as http://creativecommons.org/licenses/by/4.0/

Sponsorship

European Research Council (695671)

JW, RM, WMB, FDE, and JS acknowledge support from the Science and Technology Facilities Council (STFC), by the European Research Council (ERC) through Advanced Grant 695671 ``QUENCH'', by the UK Research and Innovation (UKRI) Frontier Research grant RISEandFALL. JW also gratefully acknowledges support from the Cosmic Dawn Center through the DAWN Fellowship. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant No. 140. BDJ, BER, FS, PAC, DJE, CNAW, and YZ acknowledge support from the JWST/NIRCam contract to the University of Arizona, NAS5-02015. BER also acknowledges support from JWST Program 3215. ST acknowledges support by the Royal Society Research Grant G125142. AJC, AJB, AS, JC, and GCJ acknowledge funding from the ``FirstGalaxies'' Advanced Grant from the ERC under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 789056). RS acknowledges support from a STFC Ernest Rutherford Fellowship (ST/S004831/1). SAl acknowledges support from the JWST MIRI Science Team Lead, grant 80NSSC18K0555, from NASA Goddard Space Flight Center to the University of Arizona. SAr acknowledges grant PID2021-127718NB-I00 funded by the Spanish Ministry of Science and Innovation/State Agency of Research (MICIN/AEI/10.13039/501100011033). This research is supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. SCa acknowledges support by European Union’s HE ERC Starting Grant No. 101040227 ``WINGS''. ECL acknowledges support of an STFC Webb Fellowship (ST/W001438/1). DJE is supported as a Simons Investigator. PGP-G acknowledges support from grant PID2022-139567NB-I00 funded by Spanish Ministerio de Ciencia e Innovaci\'on MCIN/AEI/10.13039/501100011033, FEDER, UE. H{\"U} acknowledges funding by the European Union (ERC APEX, 101164796). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. The research of CCW is supported by NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.

Relationships

Is supplemented by:

https://doi.org/10.5281/zenodo.14714293

Is derived from:

https://doi.org/10.48550/arxiv.2408.16608

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