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Dilution of chemical enrichment in galaxies 600 Myr after the Big Bang

Abstract

The evolution of galaxies throughout the last 12 Gyr of cosmic time has followed a single, universal relation that connects star-formation rates (SFRs), stellar masses (M) and chemical abundances. Deviation from this fundamental scaling relation would imply a drastic change in the processes that regulate galaxy evolution. Observations have suggested the possibility that this relation may be broken in the very early Universe. However, until recently, chemical abundances of galaxies could be measured reliably only as far back as redshift z = 3.3. With the James Webb Space Telescope, we can now characterize the SFR, M and chemical abundances of galaxies during the first few hundred million years after the Big Bang, at redshifts z = 7–10. We show that galaxies at this epoch follow unique SFR–M–main-sequence and mass–metallicity scaling relations, but their chemical abundance is one-fourth of that expected from the fundamental–metallicity relation of later galaxies. These findings suggest that galaxies at this time are still intimately connected with the intergalactic medium and subject to continuous infall of pristine gas, which effectively dilutes their metal abundances.

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Fig. 1: Imaging and spectroscopic data of CEERS-z7382.
Fig. 2: The star-forming galaxy SFR–M main sequence at redshifts z = 7–10.
Fig. 3: The mass-metallicity relation of galaxies at redshifts z = 7–10.
Fig. 4: The fundamental-metallicity relation of galaxies at redshifts z = 7–10.

Data availability

The JWST imaging and spectroscopic data are publicly available on the JWST MAST archive at https://mast.stsci.edu. The data has been processed using public software codes grizli v.1.8.3 (ref. 32) and msaexp v.0.6.7 (refs. 33,60). The reduced data are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank D. Ceverino for his insight and suggestions on interpreting the FirstLight simulation output. We further acknowledge the GLASS, CEERS and UNCOVER collaborations; we are grateful they made their early data publicly available. K.E.H. acknowledges support from the Carlsberg Foundation Reintegration Fellowship Grant CF21-0103. C.A.M. and A.H. acknowledge support by the VILLUM FONDEN under grant no. 37459. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant no. 140. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. 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.

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K.E.H. wrote the manuscript and led the analysis. G.B.B. reduced and extracted the photometric and spectroscopic data. C.G.-A. and V.B.S. performed the SED modelling. All authors contributed to the manuscript and aided in the analyses and interpretations.

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Correspondence to Kasper E. Heintz.

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Heintz, K.E., Brammer, G.B., Giménez-Arteaga, C. et al. Dilution of chemical enrichment in galaxies 600 Myr after the Big Bang. Nat Astron 7, 1517–1524 (2023). https://doi.org/10.1038/s41550-023-02078-7

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