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A population of red candidate massive galaxies ~600 Myr after the Big Bang


Galaxies with stellar masses as high as roughly 1011 solar masses have been identified1,2,3 out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1–5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 1010 solar masses) at 7.4 ≤ z ≤ 9.1, 500–700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 1011 solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.

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Fig. 1: Redshifts and tentative stellar masses of double-break selected galaxies.
Fig. 2: Images of the six galaxies with the highest apparent masses as a function of wavelength.
Fig. 3: SEDs and stellar population model fits.
Fig. 4: Cumulative stellar mass density, if the fiducial masses of the JWST-selected red galaxies are confirmed.

Data availability

The HST data are available in the MAST (, under program ID 1345. Photometry, EAZY template set, fiducial redshifts and stellar masses of the sources presented here are available at

Code availability

Publicly available codes and standard data reduction tools in the Python environments were used: Grizli4, EAZY5, astropy63, photutils64 and Prospector17,36,37.


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We are grateful to the CEERS team for providing these exquisite public JWST data so early in the mission. We thank M. Boylan-Kolchin for helpful discussions on the theoretical context of this work. Cloud-based data processing and file storage for this work is provided by the AWS Cloud Credits for Research program. The Cosmic DAWN Center is funded by the Danish National Research Foundation. K.W. wishes to acknowledge funding from Alfred P. Sloan Foundation grant no. FG-2019-12514. M.S. acknowledges project no. PID2019-109592GB-I00/AEI/10.13039/501100011033 from the Spanish Ministerio de Ciencia e Innovacion - Agencia Estatal de Investigacion.

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Authors and Affiliations



I.L. performed the photometry, devised the selection method and led the analysis. P.v.D. drafted the main text. I.L. wrote the Methods section and produced the figures. G.B. developed the image processing pipeline and created the image mosaics. E.N. and R.B. identified the first double-break galaxy, prompting the systematic search for these objects. J.L., B.W., K.A.S. and E.M. ran the Prospector analysis. All authors contributed to the manuscript and aided the analysis and interpretation.

Corresponding author

Correspondence to Ivo Labbé.

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The authors declare no competing interests.

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Nature thanks James Dunlop and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Systematic offsets in photometry as a function of wavelength.

The offsets are estimated by the ratio of the observed fluxes to the EAZY best-fit model fluxes for 5,000–10,000 sources at 0.1 < z < 5 in the CEERS field. The offsets are calculated separately for each detector (1–4), module (A/B), and filter. Symbols are slightly spread out in wavelength for clarity. a. The first in-flight NIRCam flux calibration update of 29 July 2022 (jwst_0942.pmap) introduced significant offsets in NIRCam short-wavelength zeropoints. b. After adopting our fiducial zeropoints, residual offsets are ~<3% across all bands. This paper adopts a 5% minimum systematic error for all photometric redshift and stellar population fits.

Extended Data Fig. 2 Images of the seven galaxies with apparent lowest mass.

The galaxies satisfy the color-color selection and have fiducial masses log(M*/M) < 10. The layout and panels of the figure are identical to Fig. 2 in the main text. Each cutout has a size of 2.4″ × 2.4″. The filters range from the 0.6 μm F606W filter of HST/ACS to the 4.4 μm F444W JWST/NIRCam filter.

Extended Data Fig. 3 Spectral energy distributions of all 13 galaxies that satisfy the color-color selection.

a.The layout of the figure is identical to Fig. 3a in the main text. In addition, an alternative model fit (model E, see Methods) is shown that produces low stellar masses (blue), but generally requires extremely young ages (<5 Myr) at specific narrow redshift intervals. b.The panel at the lower right shows the averaged rest-frame SED of the seven galaxies with fiducial log(M*/M) < 10, compared to previously-found galaxies at similar redshifts (see Fig. 3).


Extended Data Fig. 4 Results of the stellar population fitting.

Masses (a), redshifts (b), and the chi-squared fit quality (c) of the 13 galaxies that satisfy the color-color selection. For each galaxy seven different measurements are shown, as well as the median of the seven that is adopt as the fiducial value (see Methods section). These medians are listed in Extended Data Table 2.

Extended Data Fig. 5 Color difference between emission line and continuum-dominated models.

The line-dominated model is a 5 Myr old constant SFH with nebular emission lines. The continuum dominated model is a 50 Myr old CSF without emission lines. Two colors differences involving the line-sensitive F410M filter are shown: F356W-F410M (green) and F410M-F444W (red) and the sum of their absolute values. When Hα and Hβ+[OIII] move through the filters with redshift, the emission line sensitive medium-band F410M filter produces a strong signature, except at z = 5.6, 6.9, 7.7, where the lines transition between filters. Here continuum and line-dominated SEDs produce similar colors due to undersampling of the SED by the filters.

Extended Data Fig. 6 Stacked redshift probability distribution of all 13 galaxies in the sample.

The P(z) were derived using Bagpipes (as described in Methods). Redshifts of a high mass solution are shown in red (model B: Salim dust attenuation law, rising SFH, linear age prior, continuum dominated) and a low mass solution are shown in blue (model E: SMC dust, logarithmic age prior, emission line dominated). Other high mass fits (e.g., Prospector, EAZY) and low mass fits produce similar P(z). Solid curves show expected selection function under the assumption of continuum (red) or line-dominated models (blue). The high-mass continuum-dominated P(z) broadly traces the expected selection functions. The low-mass line-dominated P(z) is not expected for selection of a line-dominated model. The P(z) is concentrated at narrow redshifts around z = 5.6, 6.9, 7.7 (black dotted lines) where the line-sensitive F410M cannot distinguish between continuum and strong lines due to aliasing.

Extended Data Table 1 HST/ACS and JWST/NIRCam Photometry of the double break sample
Extended Data Table 2 Fiducial redshifts and stellar masses of the double break sample

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Labbé, I., van Dokkum, P., Nelson, E. et al. A population of red candidate massive galaxies ~600 Myr after the Big Bang. Nature 616, 266–269 (2023).

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