During the first 500 million years of cosmic history, the first stars and galaxies formed, seeding the Universe with heavy elements and eventually reionizing the intergalactic medium1,2,3. Observations with the James Webb Space Telescope (JWST) have uncovered a surprisingly high abundance of candidates for early star-forming galaxies, with distances (redshifts, z), estimated from multiband photometry, as large as z ≈ 16, far beyond pre-JWST limits4,5,6,7,8,9. Although such photometric redshifts are generally robust, they can suffer from degeneracies and occasionally catastrophic errors. Spectroscopic measurements are required to validate these sources and to reliably quantify physical properties that can constrain galaxy formation models and cosmology10. Here we present JWST spectroscopy that confirms redshifts for two very luminous galaxies with z > 11, and also demonstrates that another candidate with suggested z ≈ 16 instead has z = 4.9, with an unusual combination of nebular line emission and dust reddening that mimics the colours expected for much more distant objects. These results reinforce evidence for the early, rapid formation of remarkably luminous galaxies while also highlighting the necessity of spectroscopic verification. The large abundance of bright, early galaxies may indicate shortcomings in current galaxy formation models or deviations from physical properties (such as the stellar initial mass function) that are generally believed to hold at later times.
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The JWST NIRSpec data are available from the Mikulski Archive for Space Telescopes (MAST; http://archive.stsci.edu), under programme ID 2750. The CEERS JWST imaging data are available from MAST under programme ID 1345. Reduced NIRCam data products from the CEERS team are available at https://ceers.github.io. The NOEMA data is part of programme D22AC, which will be available at http://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=B/iram/noema.
JWST NIRSpec data were reduced using the JWST pipeline (v.1.8.5, reference mapping 1088; https://github.com/spacetelescope/jwst). NIRSpec data inspection was performed using the Mosviz visualization tool43 (https://jdaviz.readthedocs.io/en/latest/mosviz/index.html). Photometric redshifts were measured using EAZY39 (https://github.com/gbrammer/eazy-photoz/). Emission line profiles were fitted and line fluxes measured using LIME68 (https://lime-stable.readthedocs.io). Three different codes were used for stellar population synthesis modelling of galaxy spectro-photometric data: Synthesizer66,67; Bagpipes54 (https://bagpipes.readthedocs.io); and Cigale60,61 (https://cigale.lam.fr). For this paper, we use a non-public version of Cigale that fits photometric and spectroscopic data together.
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P.A.H., M.D., S.L.F., J.S.K. and C.J.P. acknowledge support from NASA through the STScI ERS award JWST-ERS-1345 and the JWST-GO-2750 award. S.L.F. acknowledges support from the University of Texas at Austin. P.G.P.-G. acknowledges support from the Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 through grant PGC2018-093499-B-I00. A.C.C. acknowledges support from the Leverhulme Trust via a Leverhulme Early Career Fellowship. C.T.D., D.J.M., R.J.M. and J.S.D. acknowledge the support of the Science and Technology Facilities Council. F.C. acknowledges support from a UKRI Frontier Research Guarantee Grant (grant reference EP/X021025/1). M.H.C. acknowledges financial support from the State Research Agency (AEIMCINN) of the Spanish Ministry of Science and Innovation under the grants ‘Galaxy Evolution with Artificial Intelligence’ with reference PGC2018-100852-A-I00 and ‘BASALT’ with reference PID2021-126838NB-I00. V.F. acknowledges support from ANID through FONDECYT Postdoc 2020 project 3200340. R.A. acknowledges support from ANID through FONDECYT Regular 1202007. This work is based on observations with the NASA/ESA/CSA James Webb Space Telescope obtained from the Mikulski Archive for Space Telescopes at the STScI, which is operated by the Association of Universities for Research in Astronomy (AURA), Incorporated, under NASA contract NAS5-03127. This work is partially based on observations carried out under project number D22AC with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). R.L.L. and K.C. are both NSF Graduate Fellows. T.A.H. is a NASA Postdoctoral Fellow.
The authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 NOEMA 1.1-mm contours overlaid on the NIRCam 6″ × 6″ RGB colour image (R: F444W, G: F356W, B: F200W) around CEERS-93316 (MSA ID 0) pointed by the white arrow.
North is up and east is left. The magenta contours are drawn at 1σ intervals from ± 2σ to ± 9σ. CEERS-93316 is undetected at 1.1 mm, while robust emission from a nearby source is likely responsible for a previously reported tentative SCUBA2 detection18.
Extended Data Fig. 2 Montage of images of the galaxies targeted for MSA spectroscopy presented here.
Each frame shows a 3″ × 3″ stamp centred on the location of each galaxy, with the ID labelled. The red-green-blue image for each galaxy corresponds to the JWST/NIRCam F444W, F356W and F277W, respectively, rotated with north up and east to the left. The rectangles show the approximate location of the JWST/NIRSpec MSA slit positions.
Features and spectroscopic redshifts are indicated, except for MSA ID 69 where we cannot determine a redshift with confidence. The shaded grey area corresponds to 1σ uncertainties.
Extended Data Fig. 4 2D and 1D NIRSpec spectra of CEERS-93316, CEERS-DSFG-1 and two other galaxies at similar redshifts z ≈ 4.9, highlighting a potential overdensity in the field at this redshift.
The two horizontal yellow lines in the 2D spectra indicate the extraction aperture used to measure the 1D spectra. Dotted purple vertical lines indicate the location of several emission lines when present. The shaded grey area corresponds to 1σ uncertainties in the 1D spectra and the zero flux level is marked by a dashed black horizontal line.
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Arrabal Haro, P., Dickinson, M., Finkelstein, S.L. et al. Confirmation and refutation of very luminous galaxies in the early Universe. Nature 622, 707–711 (2023). https://doi.org/10.1038/s41586-023-06521-7