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A post-starburst pathway for the formation of massive galaxies and black holes at z > 6

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Abstract

Understanding the rapid formation of supermassive black holes in the early Universe requires insights into stellar mass growth in host galaxies. Here we present NIRSpec rest-frame optical spectra and NIRCam imaging from JWST of two galaxies at z > 6, both hosting moderate-luminosity quasars. These galaxies exhibit Balmer absorption lines, like low-redshift post-starburst galaxies. Our analyses of the medium-resolution spectra and multiband photometry show that the bulk of the stellar mass (log(M*/M☉) ≥ 10.6) formed in starburst episodes at redshift 9 and 7. One of the galaxies shows a clear Balmer break and lacks spatially resolved Hα emission. It falls well below the star-formation main sequence at z = 6, indicating quiescence. The other is transitioning to quiescence; together, these massive galaxies are among the most distant post-starburst systems known. The blueshifted wings of the quasar [O iii] emission lines indicate quasar-driven outflow, which possibly influences star formation. Direct stellar velocity dispersion measurements reveal that one galaxy follows the local black hole mass versus σ* relation whereas the other is overmassive. The existence of massive post-starburst galaxies hosting billion-solar-mass black holes in short-lived quasar phases indicates that supermassive black holes and host galaxies played a principal role in each other’s rapid early formation.

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Fig. 1: JWST NIRSpec G395M spectra of J2236+0032 and J1512+4422.
Fig. 2: Quiescence of the two quasar host galaxies.
Fig. 3: Growth pathways of the two quasar host galaxies and their SMBHs.
Fig. 4: Stellar velocity dispersion (σ*) measurements.

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Data availability

The JWST data used in this paper (GO 1967 and GO 3859) can be accessed via the Mikulski Archive for Space Telescopes (https://doi.org/10.17909/mccv-p954).

Code availability

The JWST data were processed with the JWST calibration pipeline (https://jwst-pipeline.readthedocs.io). Public tools were used for data analyses: galight36 and QSOFitMORE42.

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Acknowledgements

We thank A. C. Carnall for supporting our use of Bagpipes. We thank Y. Fu for his help on the use of QSOFitMORE. We thank J. Greene, S. Toft, T. Kakimoto and M. Tanaka for fruitful discussions. This work is based on observations made with the NASA/ESA/CSA JWST. 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, under NASA contract NAS 5-03127 for JWST. These observations are associated with programmes GO 1967 and GO 3859. Support for these programmes was provided by NASA through a grant from the Space Telescope Science Institute. This work was supported by World Premier International Research Center Initiative, MEXT, Japan. This work used computing resources at Kavli IPMU. M.O., X.D., J.D.S., Y.M., T.I., K. Ito, K.K. and H.U. are supported by the Japan Society for the Promotion of Science (KAKENHI Grant Numbers JP24K22894, JP22K14071, JP18H01251, JP22H01262, JP21H04494, JP20K14531, JP23K13141, JP17H06130 and JP20H01953). M.O. and K. Inayoshi acknowledge support from the National Natural Science Foundation of China (Grant Numbers 12150410307, 12073003, 11721303, 11991052 and 11950410493). K. Inayoshi acknowledges support from the China Manned Space Project (Grant Numbers CMS-CSST-2021-A04 and CMS-CSST-2021-A06). S.E.I.B. is funded by the Deutsche Forschungsgemeinschaft (German Research Foundation) under Emmy Noether Grant Number BO 5771/1-1. Z.H., T.T. and M.S. acknowledge support from the NSF (Grant Numbers AST-2006176, AST-1907208 and AST-2006177). A.L. acknowledges funding from MUR (Grant Number PRIN 2022935STW). B.T. acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement Number 950533) and from the Israel Science Foundation (Grant Number 1849/19). F. Walter acknowledges support from the ERC (Grant Cosmic_gas). J.-T.S. is supported by the Deutsche Forschungsgemeinschaft (Project Number 518006966). M.T. acknowledges support from the NWO (Grant Number 0.16.VIDI.189.162, ODIN). S.F. acknowledges support from NASA through the NASA Hubble Fellowship (Grant Number HST-HF2-51505.001-A awarded by the Space Telescope Science Institute). K. Iwasawa acknowledges support under Grant Number PID2022-136827NB-C44 funded by MCIN/AEI/10.13039/501100011033 /FEDER, EU. M. Vestergaard gratefully acknowledges financial support from the Independent Research Fund Denmark (Grant Numbers DFF 8021-00130 and 3103-00146). F. Wang acknowledges support from the NSF (Award Number AST-2513040). R.B. is supported by the SNSF through the Ambizione Grant PZ00P2_223532.

Author information

Authors and Affiliations

  1. Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Japan

    Masafusa Onoue, Xuheng Ding & John D. Silverman

  2. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China

    Masafusa Onoue & Kohei Inayoshi

  3. Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Japan

    Masafusa Onoue & John D. Silverman

  4. Max-Planck-Institut für Astronomie, Heidelberg, Germany

    Masafusa Onoue, Sarah E. I. Bosman, Melanie Habouzit, Knud Jahnke & Fabian Walter

  5. Waseda Institute for Advanced Study (WIAS), Waseda University, Tokyo, Japan

    Masafusa Onoue

  6. School of Physics and Technology, Wuhan University, Wuhan, China

    Xuheng Ding

  7. Department of Astronomy, School of Science, The University of Tokyo, Tokyo, Japan

    John D. Silverman, Takuma Izumi, Kei Ito, Junya Arita, Nobunari Kashikawa & Kazuhiro Shimasaku

  8. Center for Astrophysical Sciences, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA

    John D. Silverman

  9. Research Center for Space and Cosmic Evolution, Ehime University, Matsuyama, Japan

    Yoshiki Matsuoka & Tohru Nagao

  10. National Astronomical Observatory of Japan, Tokyo, Japan

    Takuma Izumi, Masatoshi Imanishi & Yoshiki Toba

  11. Graduate Institute for Advanced Studies, SOKENDAI, Tokyo, Japan

    Takuma Izumi & Masatoshi Imanishi

  12. Kagoshima University, Kagoshima, Japan

    Takuma Izumi

  13. Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA

    Michael A. Strauss, Charlotte Ward & Camryn L. Phillips

  14. Cosmic Dawn Center (DAWN), Copenhagen, Denmark

    Kei Ito

  15. DTU Space, Technical University of Denmark, Kongens Lyngby, Denmark

    Kei Ito

  16. Department of Physics, TUM School of Natural Sciences, Technical University of Munich, Garching, Germany

    Irham T. Andika

  17. Max-Planck-Institut für Astrophysik, Garching, Germany

    Irham T. Andika

  18. Subaru Telescope, National Astronomical Observatory of Japan, Hilo, HI, USA

    Kentaro Aoki

  19. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan

    Shunsuke Baba

  20. Department of Astrophysics, University of Zurich, Zurich, Switzerland

    Rebekka Bieri

  21. Institute for Theoretical Physics, Heidelberg University, Heidelberg, Germany

    Sarah E. I. Bosman

  22. MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA

    Anna-Christina Eilers

  23. Department of Astronomy, The University of Texas at Austin, Austin, TX, USA

    Seiji Fujimoto

  24. Department of Astronomy, University of Geneva, Chemin d’Ecogia, CH-1290 Versoix, Switzerland

    Melanie Habouzit

  25. Department of Astronomy, Columbia University, New York, NY, USA

    Zoltan Haiman & Matthew T. Scoggins

  26. Department of Physics, Columbia University, New York, NY, USA

    Zoltan Haiman

  27. Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria

    Zoltan Haiman

  28. Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Barcelona, Spain

    Kazushi Iwasawa

  29. ICREA, Barcelona, Spain

    Kazushi Iwasawa

  30. Research Center for the Early Universe, The University of Tokyo, Tokyo, Japan

    Nobunari Kashikawa, Kotaro Kohno & Kazuhiro Shimasaku

  31. Graduate School of Science and Engineering, University of Toyama, Toyama, Japan

    Toshihiro Kawaguchi

  32. Institute of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo, Japan

    Kotaro Kohno

  33. W. M. Keck Observatory, Kamuela, HI, USA

    Chien-Hsiu Lee

  34. Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL, USA

    Junyao Li

  35. Dipartimento di Scienza e Alta Tecnologia, Università degli Studi dell’Insubria, Como, Italy

    Alessandro Lupi

  36. Steward Observatory, University of Arizona, Tucson, AZ, USA

    Jianwei Lyu, Marianne Vestergaard & Haowen Zhang

  37. Leiden Observatory, Leiden University, Leiden, the Netherlands

    Roderik Overzier & Bram Venemans

  38. Hamburger Sternwarte, University of Hamburg, Hamburg, Germany

    Jan-Torge Schindler

  39. Universität Potsdam, Potsdam, Germany

    Malte Schramm

  40. Department of Physical Sciences, Ritsumeikan University, Kusatsu, Japan

    Yoshiki Toba

  41. Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan

    Yoshiki Toba

  42. School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel

    Benny Trakhtenbrot

  43. Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands

    Maxime Trebitsch

  44. Department of Physics and Astronomy, University of California, Los Angeles, CA, USA

    Tommaso Treu

  45. Institute for Advanced Research, Nagoya University, Nagoya, Japan

    Hideki Umehata

  46. Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan

    Hideki Umehata

  47. DARK, Niels Bohr Institute, Copenhagen, Denmark

    Marianne Vestergaard

  48. Institut d’Astrophysique de Paris, CNRS, Sorbonne Université, Paris, France

    Marta Volonteri

  49. Department of Astronomy, University of Michigan, Ann Arbor, MI, USA

    Feige Wang & Jinyi Yang

Authors
  1. Masafusa Onoue
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  2. Xuheng Ding
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  3. John D. Silverman
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  4. Yoshiki Matsuoka
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  5. Takuma Izumi
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  6. Michael A. Strauss
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  7. Charlotte Ward
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  8. Camryn L. Phillips
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  9. Kei Ito
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  10. Irham T. Andika
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  11. Kentaro Aoki
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  12. Junya Arita
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  13. Shunsuke Baba
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  14. Rebekka Bieri
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  15. Sarah E. I. Bosman
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  16. Anna-Christina Eilers
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  17. Seiji Fujimoto
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  18. Melanie Habouzit
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  19. Zoltan Haiman
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  20. Masatoshi Imanishi
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  21. Kohei Inayoshi
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  22. Kazushi Iwasawa
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  23. Knud Jahnke
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  24. Nobunari Kashikawa
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  25. Toshihiro Kawaguchi
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  26. Kotaro Kohno
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  27. Chien-Hsiu Lee
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  28. Junyao Li
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  29. Alessandro Lupi
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  30. Jianwei Lyu
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  31. Tohru Nagao
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  32. Roderik Overzier
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  33. Jan-Torge Schindler
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  34. Malte Schramm
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  35. Matthew T. Scoggins
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  36. Kazuhiro Shimasaku
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  37. Yoshiki Toba
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  38. Benny Trakhtenbrot
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  39. Maxime Trebitsch
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  40. Tommaso Treu
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  41. Hideki Umehata
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  42. Bram Venemans
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  43. Marianne Vestergaard
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  44. Marta Volonteri
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  45. Fabian Walter
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  46. Feige Wang
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  47. Jinyi Yang
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  48. Haowen Zhang
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Contributions

M.O. led the preparation of the observation programme, data reduction, spectroscopic data analysis and preparing the paper. X.D. led the imaging data analysis and contributed to the relevant sections of the paper. We regard these first two authors (M.O. and X.D.) as having contributed equally to this work. J.D.S. and M.A.S. provided consulting on paper preparation. Y.M. contributed to the discovery of the two quasars analysed in this paper. C.W. led the spectral analysis of the double-peak line shape of the Hα emission in the spectrum of J1512+4422. C.L.P. performed the NIRSpec 2D spectroscopic analysis and evaluated the strength of the extended Hα emission. M.T.S. and H.Z. provided theoretical model predictions on the SMBH and host stellar growth history of J2236+0032 presented in Fig. 3. K. Ito contributed to the SED analysis of the two galaxies based on pPXF. M.O., X.D., J.D.S., Y.M., T.I., M.A.S., C.L.P. and K.J. led the project design and management and also developed the main interpretation of the results. I.T.A., K.A., J.A., S.B., R.B., S.E.I.B., A.-C.E., S.F., M.H., Z.H., M.I., K. Inayoshi, K. Iwasawa, N.K., T.K., K.K., C.-H.L., J. Li, A.L., J. Lyu, T.N., R.O., J.-T.S., M.S., K.S., Y.T., B.T., M.T., T.T., H.U., B.V., M. Volonteri, M. Vestergaard, F. Walter, F. Wang and J.Y contributed to the discussion of the results presented and to paper preparation.

Corresponding authors

Correspondence to Masafusa Onoue or Xuheng Ding.

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Competing interests

The authors declare no competing interests.

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Nature Astronomy thanks Francesco D’Eugenio, Minghao Yue and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 [O III] ionized gas profile.

Left and right panels show the spectrum of J2230 + 0032 and J1512 + 4422, respectively (black). The best-fit models for the continuum, iron, and Hβ line emissions are subtracted for illustration purposes. The core and broad wing components modeled as Gaussian profiles are shown with blue and orange lines, respectively. The total profiles of the best-fit emission line models are shown with red lines. The rest-frame wavelengths indicated at the top, as well as the expected locations of each doublet line (grey dashed lines) are based on redshifts estimated from the Balmer absorption lines. In the bottom panels, the residuals are shown in black lines, and the ± 1σ flux uncertainty at each pixel is indicated as grey shades.

Extended Data Fig. 2 Double-peaked Hα emission for J1512 + 4422.

The observed Hα profile (after continuum subtraction) is shown in black. Our model fit based on the method presented in ref. 59 is shown as colored lines (dark blue: disk model, light blue: narrow lines, red: total). The wavelength and the flux density are presented in the rest frame. The bottom panel shows the residual fluxes, that is, the difference between the observed profile and the best-fit model.

Extended Data Fig. 3 Host galaxy detection of J2236 + 0032 (top) and J1512 + 4422 (bottom).

For each quasar, we present the original NIRCam image, the PSF-subtracted host galaxy-only image, and the best-fit host galaxy model in a vertical order. Data are presented from F115W filter to F480M for J2236+0032, and F150W and F356W for J1512+4422. The image scale of each panel is 2″ × 2″, with flux density shown on a logarithmic scale in units of megajansky per steradian. Arrows in the lower left panels indicate the North and East directions.

Extended Data Fig. 4 NIRSpec Fixed-Slit alignment onto the host galaxies.

For each galaxy, the outer rectangle indicates the S200A2 slit position and the inner rectangle indicates the extraction aperture of the 1D spectrum. The background images are the decomposed host images in F356W.

Extended Data Fig. 5 Example posterior distribution of the Bagpipes SED fitting.

The top and bottom panels show J2236 + 0032, and J1512 + 4422, respectively. The delayed-τ SFH model is presented for each galaxy. Note that the stellar mass fitted in Bagpipes (\(\log {M}_{* ,{\rm{formed}}}\)) represents the total formed stellar mass, from which the observed stellar mass (\(\log {M}_{* }\)) is derived.

Extended Data Fig. 6 Comparison of spectral fitting results using two different methods.

The top and bottom panels show the decomposed host spectrum (light blue) for J2236 + 0032 and J1512 + 4422, respectively. The best-fit models from Bagpipes (dark blue) and pPXF (orange) are overlaid. The red wing of the Hγ absorption of J1512 + 4422, shown as gray shade, is masked in the spectral fitting.

Extended Data Table 1 [O III] line profile
Full size table
Extended Data Table 2 NIRCam photometry of the two quasars and their host galaxies
Full size table
Extended Data Table 3 Host effective radius Reff and minor-to-major axis ratio q(= b/a) in F356W
Full size table
Extended Data Table 4 Quasar and Host SED parameters obtained from Bagpipes and pPXF
Full size table

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Onoue, M., Ding, X., Silverman, J.D. et al. A post-starburst pathway for the formation of massive galaxies and black holes at z > 6. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02628-1

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