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A massive galaxy that formed its stars at z ≈ 11


The formation of galaxies by gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental paradigm underpinning modern astrophysics1,2 and predicts a strong decline in the number of massive galaxies at early cosmic times3,4,5. Extremely massive quiescent galaxies (stellar masses of more than 1011M) have now been observed as early as 1–2 billion years after the Big Bang6,7,8,9,10,11,12,13. These galaxies are extremely constraining on theoretical models, as they had formed 300–500 Myr earlier, and only some models can form massive galaxies this early12,14. Here we report on the spectroscopic observations with the JWST of a massive quiescent galaxy ZF-UDS-7329 at redshift 3.205 ± 0.005. It has eluded deep ground-based spectroscopy8, it is significantly redder than is typical and its spectrum reveals features typical of much older stellar populations. Detailed modelling shows that its stellar population formed around 1.5 billion years earlier in time (z ≈ 11) at an epoch when dark matter halos of sufficient hosting mass had not yet assembled in the standard scenario4,5. This observation may indicate the presence of undetected populations of early galaxies and the possibility of significant gaps in our understanding of early stellar populations, galaxy formation and the nature of dark matter.

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Fig. 1: The JWST NIRSpec spectrum of galaxy ZF-UDS-7329.
Fig. 2: The effect of age and metallicity on stellar populations.
Fig. 3: Comparison of SFHs with dark matter halo assembly histories.

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Data availability

The full JWST spectrum of ZF-UDS-7329 and associated LSF are available in CSV format as Source Data for Figs. 1 and  2 and Extended Data Fig. 2. The photometry is given in Extended Table 1. The wavelength units are in micrometres (observed frame) and the flux units are 10−19 ergs cm−2 s−1 Å−2 s−1. Source data are provided with this paper.

Code availability

All software packages used in this analysis are publicly available. In particular FAST++, Prospector-α and the hmf Python module are available from GitHub.


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K.G. thanks R. Abraham for assistance in fetching data on z = 0 comparison galaxies from Canadian archives and J. Brinchmann for inspiring discussions on the 0.94 μm bump. This work is based on observations made with JWST, which is run by NASA, the European Space Agency and the Canadian Space Agency. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programme 2565. We thank the JWST team for all their hard work, which made this great observatory possible. We thank M. Maseda and A. Strom for helpful discussions during the data reduction process. T.N., K.G. and C.J. acknowledge support from an Australian Research Council Laureate Fellowship (FL180100060). This work has benefited from funding from the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (Project No. CE170100013). C.P. acknowledges generous support from Marsha L. and Ralph F. Schilling and from the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy. The Cosmic Dawn Center is funded by the Danish National Research Foundation (Grant No. DNRF140). P.O. is supported by the Swiss National Science Foundation (Project Grant No. 200020_207349). This work received funding from the Swiss State Secretariat for Education, Research and Innovation.

Author information

Authors and Affiliations



K.G. did all the final data analysis, made the figures and wrote the manuscript. T.N. reduced the NIRSpec data and ran FAST++ and Prospector model fits. C.S. originally identified ZF-UDS-7329 as an interesting object in S18 and analysed deep ground-based spectra that failed to secure a redshift but motivated the JWST programme. C.S. added the LSF functionality to the FAST++ and slinefit codes for this paper. C.L. and A.C.-G. provided the comparisons with halos in simulations. L.K. processed the NIRCam data. H.C. did the TNG300 and THESAN comparisons. All other authors contributed to the scientific discussions in the proposal and manuscript.

Corresponding author

Correspondence to Karl Glazebrook.

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Nature thanks James Dunlop and Chris Hayward for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Flux calibration of the NIRSpec spectrum.

The lower blue curve shows the derived flux through the slit, compared with NIRCAM photometry with a synthetic slit aperture. This shows very good agreement. The upper grey curve shows the correction of the spectrum to total NIRCAM photometry. Both spectra show have flux error bars superimposed. The inset shows the MSA shutter footprint overlaid on the NIRCAM F200W image.

Extended Data Fig. 2 Comparison of spectra at longer wavelengths.

ZF-UDS-7329 in the rest frame 0.7–1.3 μm region is compared to redshifted high signal:noise spectra52 of the nuclei of local NGC galaxies (these are normalised to the same flux at 0.9–0.95 μm rest and then offset for clarity). NGC 5850 is a nearby spiral with a luminosity weighted age of ~ 5 Gyr, and it can be seen that the 0.94 μm absorption (ZrO, CN, TiO bands) is quite similar, and there is overall a very good match between them to the bumps and wiggles in the continuum which arise from numerous molecular bands in cool stars. NGC205’s light is dominated by an intermediate age population (0.1–1 Gyr) and it can be seen that the 0.94 μm feature, and other molecular bands are much weaker. Note the flux axis is greatly zoomed compared to Fig. 1 to highlight very weak absorption features.

Extended Data Fig. 3 Comparison of star formation histories with dark matter halo assembly histories for high metal abundance.

This is a version of Fig. 3 where we force fit the poor fit model with [Fe/H] = 0.05. The age is reduced to ~ 1 Gyr but is still significantly discrepant with theoretical expectations. Colours, lines and symbols are as in Fig. 3.

Extended Data Table 1 NIRCAM integrated photometry for ZF-UDS-7329

Source data

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Glazebrook, K., Nanayakkara, T., Schreiber, C. et al. A massive galaxy that formed its stars at z ≈ 11. Nature 628, 277–281 (2024).

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