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Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6


The existence of massive (1011 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z > 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower4. The only known galaxies with very high star-formation rates at z > 6 are, with one exception5, the host galaxies of quasars6,7,8,9, but these galaxies also host accreting supermassive (more than 109 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C ii] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift10,11,12. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations13,14. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.

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Figure 1: Images and spectra of the quasars and their companion galaxies discovered in this study.
Figure 2: Velocity structure in the system PJ308−21.
Figure 3: Intensely star-forming galaxies in the earliest galactic overdensities.


  1. 1

    Straatman, C. M. S. et al. A substantial population of massive quiescent galaxies at z ~ 4 from ZFOURGE. Astrophys. J. 783, L14 (2014)

    ADS  Article  Google Scholar 

  2. 2

    Nayyeri, H. et al. A study of massive and evolved galaxies at high redshift. Astrophys. J. 794, 68 (2014)

    ADS  Article  Google Scholar 

  3. 3

    Whitaker, K. E. et al. Quiescent galaxies in the 3D-HST survey: spectroscopic confirmation of a large number of galaxies with relatively old stellar populations at z ~ 2. Astrophys. J. 770, L39 (2013)

    ADS  Article  Google Scholar 

  4. 4

    Bouwens, R. J. et al. UV luminosity functions at redshifts z ~ 4 to z ~ 10: 10,000 galaxies from HST legacy fields. Astrophys. J. 803, 34 (2015)

    ADS  Article  Google Scholar 

  5. 5

    Riechers, D. et al. A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34. Nature 496, 329–333 (2013)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Bertoldi, F. et al. Dust emission from the most distant quasars. Astron. Astrophys. 406, L55–L58 (2003)

    ADS  Article  Google Scholar 

  7. 7

    Walter, F. et al. A kiloparsec-scale hyper-starburst in a quasar host less than 1 gigayear after the Big Bang. Nature 457, 699–701 (2009)

    ADS  CAS  Article  Google Scholar 

  8. 8

    Wang, R. et al. Star formation and gas kinematics of quasar host galaxies at z ~ 6: new insights from ALMA. Astrophys. J. 773, 44 (2013)

    ADS  Article  Google Scholar 

  9. 9

    Carilli, C. L. & Walter, F. Cool gas in high-redshift galaxies. Annu. Rev. Astron. Astrophys. 51, 105–161 (2013)

    ADS  CAS  Article  Google Scholar 

  10. 10

    Omont, A. et al. Molecular gas and dust around a radio-quiet quasar at redshift 4.69. Nature 382, 428–431 (1996)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Trakhtenbrot, B. et al. ALMA observations show major mergers among the host galaxies of fast-growing, high-redshift supermassive black holes. Astrophys. J. 836, 8 (2017)

    ADS  Article  Google Scholar 

  12. 12

    Riechers, D. A. et al. ALMA imaging of gas and dust in a galaxy protocluster at redshift 5.3: [C ii] emission in “typical” galaxies and dusty starbursts ≈1 billion years after the Big Bang. Astrophys. J. 796, 84 (2014)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Narayanan, D. et al. The formation of submillimetre-bright galaxies from gas infall over a billion years. Nature 525, 496–499 (2015)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Habouzit, M., Volonteri, M., Latif, M., Dubois, Y. & Peirani, S. On the number density of ‘direct collapse’ black hole seeds. Mon. Not. R. Astron. Soc. 463, 529–540 (2016)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Herrera-Camus, R. et al. [C ii] 158 μm emission as a star formation tracer. Astrophys. J. 800, 1 (2015)

    ADS  Article  Google Scholar 

  16. 16

    De Looze, I. et al. The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types. Astron. Astrophys. 568, A62 (2014)

    Article  Google Scholar 

  17. 17

    Bañados, E. et al. The Pan-STARRS1 distant z > 5.6 quasar survey: more than 100 quasars within the first Gyr of the universe. Astrophys. J. Suppl. Ser. 227, 11 (2016)

    ADS  Article  Google Scholar 

  18. 18

    Walter, F. et al. ALMA spectroscopic survey in the Hubble Ultra Deep Field: survey description. Astrophys. J. 833, 67 (2016)

    ADS  Article  Google Scholar 

  19. 19

    Bothwell, M. S. et al. A survey of molecular gas in luminous sub-millimetre galaxies. Mon. Not. R. Astron. Soc. 429, 3047–3067 (2013)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Beelen, A. et al. 350 μm dust emission from high-redshift quasars. Astrophys. J. 642, 694–694 (2006)

    ADS  CAS  Article  Google Scholar 

  21. 21

    Downes, D. et al. Submillimeter spectrum and dust mass of the primeval galaxy IRAS 10214+4724. Astrophys. J. 398, L25–L27 (1992)

    ADS  Article  Google Scholar 

  22. 22

    Berta, S., Lutz, D., Genzel, R., Förster-Schreiber, N. M. & Tacconi, L. J. Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA. Astron. Astrophys. 587, A73 (2016)

    ADS  Article  Google Scholar 

  23. 23

    Farrah, D. et al. Far-infrared fine-structure line diagnostics of ultraluminous infrared galaxies. Astrophys. J. 776, 38 (2013)

    ADS  Article  Google Scholar 

  24. 24

    Malhotra, S. et al. Far-infrared spectroscopy of normal galaxies: physical conditions in the interstellar medium. Astrophys. J. 561, 766–786 (2001)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Aravena, M. et al. The ALMA spectroscopic survey in the Hubble Ultra Deep Field: search for [C ii] line and dust emission in 6 < z < 8 galaxies. Astrophys. J. 833, 71 (2016)

    ADS  Article  Google Scholar 

  26. 26

    Swinbank, A. M. et al. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field-South: detection of [C ii] at z = 4.4. Mon. Not. R. Astron. Soc. 427, 1066–1074 (2012)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Garcia-Vergara, C., Hennawi, J. F., Barrientos, L. F. & Rix, H.-W. Strong clustering of Lyman break galaxies around luminous quasars at z~4. Preprint at (2017)

  28. 28

    Bouwens, R. J. et al. ALMA spectroscopic survey in the Hubble Ultra Deep Field: the infrared excess of UV-selected z = 2–10 galaxies as a function of UV-continuum slope and stellar mass. Astrophys. J. 833, 72 (2016)

    ADS  Article  Google Scholar 

  29. 29

    Capak, P. L. et al. Galaxies at redshifts 5 to 6 with systematically low dust content and high [C ii] emission. Nature 522, 455–458 (2015)

    ADS  CAS  Article  Google Scholar 

  30. 30

    Kennicutt, R. C. & Evans, N. J. Star formation in the Milky Way and nearby galaxies. Annu. Rev. Astron. Astrophys. 50, 531–608 (2012)

    ADS  CAS  Article  Google Scholar 

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We thank J. Hennawi, Y. Shen, A. Myers and L. Guzzo for comments on the QSO clustering. Support for R.D. was provided by the DFG priority programme 1573 “The physics of the interstellar medium.” F.W., B.V. and E.P.F. acknowledge support through ERC grant COSMIC-DAWN. R.W. acknowledges support from the National Science Foundation of China (NSFC; grant numbers 11473004 and 11533001) and the National Key Program for Science and Technology Research and Development (grant 2016YFA0400703). ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (South Korea), in cooperation with Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. E.B. is a Carnegie-Princeton Fellow.

Author information




R.D. led the writing and analysis. F.W. was principle investigator of the ALMA programme that led to this discovery. F.W. and B.P.V. played a central part in the project design and implementation. E.P.F. provided the clustering analysis. E.B., B.P.V., E.P.F., C.M., F.W. and H.W.R. contributed to the identification of Pan-STARRS1 quasars. X.F. provided the Hubble observations of J0842+1218. All authors contributed to writing the proposal, and reviewed, discussed and commented on the manuscript.

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Correspondence to R. Decarli.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks D. Frayer and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Decarli, R., Walter, F., Venemans, B. et al. Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6. Nature 545, 457–461 (2017).

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