A dusty star-forming galaxy at z = 6 revealed by strong gravitational lensing


Since their discovery, submillimetre-selected galaxies1,2 have revolutionized the field of galaxy formation and evolution. From the hundreds of square degrees mapped at submillimetre wavelengths3,4,5, only a handful of sources have been confirmed to lie at z > 5 (refs 6,7,8,9,10) and only two at z ≥ 6 (refs 11,12). All of these submillimetre galaxies are rare examples of extreme starburst galaxies with star formation rates of 1,000 M yr−1 and therefore are not representative of the general population of dusty star-forming galaxies. Consequently, our understanding of the nature of these sources, at the earliest epochs, is still incomplete. Here, we report the spectroscopic identification of a gravitationally amplified (μ = 9.3 ± 1.0) dusty star-forming galaxy at z = 6.027. After correcting for gravitational lensing, we derive an intrinsic less-extreme star formation rate of 380 ± 50 M yr−1 for this source and find that its gas and dust properties are similar to those measured for local ultra luminous infrared galaxies, extending the local trends to a poorly explored territory in the early Universe. The star-formation efficiency of this galaxy is similar to those measured in its local analogues13, despite a ~12 Gyr difference in cosmic time.

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Fig. 1: Identification of molecular emission lines and redshift derivation.
Fig. 2: ALMA high-angular resolution continuum observations and lensing model.
Fig. 3: Photometry and SED.
Fig. 4: Star formation efficiency and [CII] deficiency.


  1. 1.

    Smail, I., Ivison, R. J. & Blain, A. W. A deep sub-millimeter survey of lensing clusters: a new window on galaxy formation and evolution. Astrophys. J. Lett. 490, L5–L8 (1997).

    ADS  Article  Google Scholar 

  2. 2.

    Hughes, D. et al. High-redshift star formation in the Hubble Deep Field revealed by a submillimetre-wavelength survey. Nature 394, 241–247 (1998).

    ADS  Article  Google Scholar 

  3. 3.

    Oliver, S. et al. The Herschel Multi-tiered Extragalactic Survey: HerMES. Mon. Not. R. Astron. Soc. 424, 1614–1635 (2012).

    ADS  Article  Google Scholar 

  4. 4.

    Valiante, E. et al. The Herschel-ATLAS data release 1 – I. Maps, catalogues and number counts. Mon. Not. R. Astron. Soc. 462, 3146–3179 (2016).

    ADS  Article  Google Scholar 

  5. 5.

    Michałowski, M. et al. The SCUBA-2 Cosmology Legacy Survey: the nature of bright submm galaxies from 2 deg2 of 850-μm imaging. Mon. Not. R. Astron. Soc. 469, 492–515 (2017).

    ADS  Article  Google Scholar 

  6. 6.

    Capak, P. et al. A massive protocluster of galaxies at a redshift of z ≈ 5.3. Nature 470, 233–235 (2011).

    ADS  Article  Google Scholar 

  7. 7.

    Combes, F. et al. A bright z = 5.2 lensed submillimeter galaxy in the field of Abell 773. HLSJ091828.6 + 514223. Astron. Astrophys. Lett. 538, L4 (2012).

    ADS  Article  Google Scholar 

  8. 8.

    Walter, F. et al. The intense starburst HDF850.1 in a galaxy overdensity at z 5.2 in the Hubble Deep Field. Nature 486, 233–236 (2012).

    ADS  Article  Google Scholar 

  9. 9.

    Ma, J. et al. Stellar masses and star formation rates of lensed, dusty, star-forming galaxies from the SPT survey. Astrophys. J. 812, 88–104 (2015).

    ADS  Article  Google Scholar 

  10. 10.

    Riechers, D. et al. Rise of the titans: a dusty, hyper-luminous ‘870 micron riser’ galaxy at z  6. Preprint at https://arxiv.org/abs/1705.09660 (2017).

  11. 11.

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

    ADS  Article  Google Scholar 

  12. 12.

    Strandet, M. et al. ISM properties of a massive dusty star-forming galaxy discovered at z 7. Astrophys. J. Lett. 842, L15 (2017).

    ADS  Article  Google Scholar 

  13. 13.

    Sanders, D. & Mirabel, I. Luminous infrared galaxies. Ann. Rev. Astron. Astrophys. 34, 749–792 (1996).

    ADS  Article  Google Scholar 

  14. 14.

    Ivison, R. et al. The space density of luminous dusty star-forming galaxies at z > 4: SCUBA-2 and LABOCA imaging of ultrared galaxies from Herschel-ATLAS. Astrophys. J. 832, 78 (2016).

    ADS  Article  Google Scholar 

  15. 15.

    Cooray, A. et al. HerMES: the rest-frame UV emission and a lensing model for the z = 6.34 luminous dusty starburst galaxy HFLS3. Astrophys. J. 790, 40–50 (2014).

    ADS  Article  Google Scholar 

  16. 16.

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

    ADS  Article  Google Scholar 

  17. 17.

    Watson, D. et al. A dusty, normal galaxy in the epoch of reionization. Nature 519, 327–330 (2015).

    ADS  Article  Google Scholar 

  18. 18.

    Willott, C., Carilli, C., Wagg, J. & Wang, R. Star formation and the interstellar medium in z > 6 UV-luminous Lyman-break galaxies. Astrophys. J. 807, 180–188 (2015).

    ADS  Article  Google Scholar 

  19. 19.

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

    ADS  Article  Google Scholar 

  20. 20.

    Oteo, I. et al. Witnessing the birth of the red sequence: ALMA high-resolution imaging of [C II] and dust in two interacting ultra-red starbursts at z = 4.425. Astrophys. J. 827, 34 (2016).

    ADS  Article  Google Scholar 

  21. 21.

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

    ADS  Article  Google Scholar 

  22. 22.

    Straatman, C. et al. The sizes of massive quiescent and star-forming galaxies at z 4 with ZFOURGE and CANDELS. Astrophys. J. Lett. 808, L29 (2015).

    ADS  Article  Google Scholar 

  23. 23.

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

    ADS  Article  Google Scholar 

  24. 24.

    Tacconi, L. et al. High molecular gas fractions in normal massive star forming galaxies in the young Universe. Nature 463, 781–784 (2010).

    ADS  Article  Google Scholar 

  25. 25.

    Greve, T. et al. Star formation relations and CO spectral line energy distributions across the J-ladder and redshift. Astrophys. J. 794, 142 (2014).

    ADS  Article  Google Scholar 

  26. 26.

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

    ADS  Article  Google Scholar 

  27. 27.

    Yang, C. et al. Submillimeter H2O and H2O + emission in lensed ultra- and hyper-luminous infrared galaxies at z = 2−4. Astron. Astrophys. 595, 80 (2016).

    Article  Google Scholar 

  28. 28.

    Wilson, C. et al. Luminous infrared galaxies with the submillimeter array. I. Survey overview and the central gas to dust ratio. Astrophys. J. Suppl. Ser. 178, 189–224 (2008).

    ADS  Article  Google Scholar 

  29. 29.

    Daz-Santos, T. et al. Explaining the [C II]157.7 μm deficit in luminous infrared galaxies—first results from a Herschel/PACS study of the GOALS sample. Astrophys. J. 774, 68 (2013).

    ADS  Article  Google Scholar 

  30. 30.

    Rodriguez-Puebla, A., Primack, J., Avila-Reese, V. & Faber, S. Constraining the galaxy-halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties. Mon. Not. R. Astron. Soc. 470, 651–687 (2017).

    ADS  Article  Google Scholar 

  31. 31.

    Sanders, D., Scoville, N. & Soifer, B. Molecular gas in luminous infrared galaxies. Astrophys. J. 370, 158–171 (1991).

    ADS  Article  Google Scholar 

  32. 32.

    Solomon, P., Downes, D., Radford, S. J. E. & Barrett, J. W. The molecular interstellar medium in ultraluminous infrared galaxies. Astrophys. J. 478, 144–161 (1997).

    ADS  Article  Google Scholar 

  33. 33.

    Aravena, M. et al. A survey of the cold molecular gas in gravitationally lensed star-forming galaxies at z > 2. Mon. Not. R. Astron. Soc. 457, 4406–4420 (2016).

    ADS  Article  Google Scholar 

  34. 34.

    Gullberg, B. et al. The nature of the [C II] emission in dusty star-forming galaxies from the SPT survey. Mon. Not. R. Astron. Soc. 449, 2883–2900 (2015).

    ADS  Article  Google Scholar 

  35. 35.

    Hughes, D. et al. The Large Millimeter Telescope. Proc. SPIE 7733, 13 (2010).

    Google Scholar 

  36. 36.

    Wilson, G. et al. The AzTEC mm-wavelength camera. Mon. Not. R. Astron. Soc. 386, 807–818 (2008).

    ADS  Article  Google Scholar 

  37. 37.

    Erickson, N. et al. An ultra-wideband receiver and spectrometer for 74–110 GHz. ASPCS 375, 71 (2007).

    ADS  Google Scholar 

  38. 38.

    Scott, K. B. et al. AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue. Mon. Not. R. Astron. Soc. 385, 12225–2238 (2008).

    Article  Google Scholar 

  39. 39.

    Yun, M. S. et al. Early science with the Large Millimeter Telescope: CO and [C II] emission in the z = 4.3 AzTEC J095942.9 + 022938 (COSMOS AzTEC-1). Mon. Not. R. Astron. Soc. 454, 3485–3499 (2015).

    ADS  Article  Google Scholar 

  40. 40.

    Savitzky, A. & Golay, M. J. E. Smoothing and differentiation of data by simplified least squares procedures. Anal. Chem. 36, 1627–1639 (1964).

    ADS  Article  Google Scholar 

  41. 41.

    Smail, I., Swinbank, A. M., Ivison, R. J. & Ibar, E. The potential influence of far-infrared emission lines on the selection of high-redshift galaxies. Mon. Not. R. Astron. Soc. Lett. 414, L95–L99 (2011).

    ADS  Article  Google Scholar 

  42. 42.

    Sault, R. J., Teuben, P. J. & Wright, M. C. H. A retrospective view of Miriad. in Astronomical Data Analysis Software and Systems IV (eds Shaw, R., Payne, H. E. & Hayes, J. J. E.) ASP Conf. Series 77, 433–436 (1995).

  43. 43.

    Oteo, I. et al. Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe. Preprint at https://arxiv.org/abs/1709.04191 (2017).

  44. 44.

    Spilker, J. et al. ALMA imaging and gravitational lens models of South Pole Telescope—selected dusty, star-forming galaxies at high redshifts. Astrophys. J. 826, 112 (2016).

    ADS  Article  Google Scholar 

  45. 45.

    Fudamoto, Y. et al. The most distant, luminous, dusty star-forming galaxies: redshifts from NOEMA and ALMA spectral scans. Mon. Not. R. Astron. Soc. 472, 2028–2041 (2017).

  46. 46.

    Lutz, D. et al. The far-infrared emitting region in local galaxies and QSOs: size and scaling relations. Astron. Astrophys. 591, 136 (2016).

    Article  Google Scholar 

  47. 47.

    Hodge, J. et al. Kiloparsec-scale dust disks in high-redshift luminous submillimeter galaxies. Astrophys. J. 833, 103 (2016).

    ADS  Article  Google Scholar 

  48. 48.

    Silva, L., Granato, G. L., Bressan, A. & Danese, L. Modeling the effects of dust on galactic spectral energy distributions from the ultraviolet to the millimeter band. Astrophys. J. 509, 103–117 (1998).

    ADS  Article  Google Scholar 

  49. 49.

    Ivison, R. et al. Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3. Astron. Astrophys. Lett. 518, L35 (2010).

    ADS  Article  Google Scholar 

  50. 50.

    Michałowski, M. J., Hjorth, J. & Watson, D. Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly. Astron. Astrophys. 514, A67 (2010).

    Article  Google Scholar 

  51. 51.

    Pope, A. et al. Mid-infrared spectral diagnosis of submillimeter galaxies. Astrophys. J. 675, 1171–1193 (2008).

    ADS  Article  Google Scholar 

  52. 52.

    Kirkpatrick, A. et al. GOODS-Herschel: impact of active galactic nuclei and star formation activity on infrared spectral energy distributions at high redshift. Astrophys. J. 759, 139 (2012).

    ADS  Article  Google Scholar 

  53. 53.

    Kennicutt, R. C. Jr The global Schmidt law in star-forming galaxies. Astrophys. J. 498, 541–552 (1998).

    ADS  Article  Google Scholar 

  54. 54.

    Chabrier, G. The galactic disk mass function: reconciliation of the Hubble Space Telescope and nearby determinations. Astrophys. J. 586, L133–L136 (2003).

    ADS  Article  Google Scholar 

  55. 55.

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

    ADS  Article  Google Scholar 

  56. 56.

    Salpeter, E. The luminosity function and stellar evolution. Astrophys. J. 121, 161 (1955).

    ADS  Article  Google Scholar 

  57. 57.

    Dunne, L. & Eales, S. A. The SCUBA Local Universe Galaxy Survey – II. 450-μm data: evidence for cold dust in bright IRAS galaxies. Mon. Not. R. Astron. Soc. Lett. 327, 697–714 (2001).

    ADS  Article  Google Scholar 

  58. 58.

    Chapin, E. et al. An AzTEC 1.1 mm survey of the GOODS-N field – II. Multiwavelength identifications and redshift distribution. Mon. Not. R. Astron. Soc. Lett. 398, 1793–1808 (2009).

    Article  Google Scholar 

  59. 59.

    Magnelli, B. et al. A Herschel view of the far-infrared properties of submillimetre galaxies. Astron. Astrophys. 539, 155 (2012).

    Article  Google Scholar 

  60. 60.

    Simpson, J. et al. The SCUBA-2 Cosmology Legacy Survey: multi-wavelength properties of ALMA-identified submillimeter galaxies in UKIDSS UDS. Astrophys. J. 839, 58 (2017).

    ADS  Article  Google Scholar 

  61. 61.

    Da Cunha, E. et al. On the effect of the cosmic microwave background in high-redshift (sub-)millimeter observations. Astrophys. J. 766, 13 (2013).

    ADS  Article  Google Scholar 

  62. 62.

    James, A., Dunne, L., Eales, S. & Edmunds, M. SCUBA observations of galaxies with metallicity measurements: a new method for determining the relation between submillimetre luminosity and dust mass. Mon. Not. R. Astron. Soc. Lett. 335, 753–761 (2002).

    ADS  Article  Google Scholar 

  63. 63.

    Dunne, L., Eales, S., Ivison, R., Morgan, H. & Edmunds, M. Type II supernovae as a significant source of interstellar dust. Nature 424, 285–287 (2003).

    ADS  Article  Google Scholar 

  64. 64.

    Da Cunha, E. et al. An ALMA survey of sub-millimeter galaxies in the Extended Chandra Deep Field South: physical properties serived from ultraviolet-to-radio modeling. Astrophys. J. 806, 110 (2015).

    ADS  Article  Google Scholar 

  65. 65.

    Solomon, P. & Vanden Bout, P. Molecular gas at high redshift. Ann. Rev. Astron. Astrophys. 43, 677–725 (2005).

    ADS  Article  Google Scholar 

  66. 66.

    Scoville, N. et al. ISM masses and the star formation law at z = 1 to 6: ALMA observations of dust continuum in 145 galaxies in the COSMOS survey field. Astrophys. J. 820, 83 (2016).

    ADS  Article  Google Scholar 

  67. 67.

    Papadopoulos, P. P. et al. The molecular gas in luminous infrared galaxies. II. Extreme physical conditions and their effects on the Xco factor. Astrophys. J. 751, 10 (2012).

    ADS  Article  Google Scholar 

  68. 68.

    Engel, H. et al. Most submillimeter galaxies are major mergers. Astrophys. J. 724, 233–243 (2010).

    ADS  Article  Google Scholar 

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We thank I. Smail for insightful comments that improved the quality of the paper. J.A.Z. acknowledges support from a Mexican Consejo Nacional de Ciencia y Tecnología studentship. R.J.I., L.D. and I.O. acknowledge support from the European Research Council in the form of the Advanced Investigator Programme, 321302, COSMICISM. L.D. additionally acknowledges support from the European Research Council Consolidator Grant CosmicDust. H.D. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness under the 2014 Ramón y Cajal programme MINECO RYC-2014-15686. M.J.M. acknowledges the support of the National Science Centre, Poland through the POLONEZ grant 2015/19/P/ST9/04010 and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement number 665778. This work would not have been possible without long-term financial support from the Mexican Consejo Nacional de Ciencia y Tecnología during the construction and early operational phase of the Large Millimeter Telescope Alfonso Serrano, as well as support from the United States National Science Foundation via the University Radio Observatory programme, the Instituto Nacional de Astrofísica, Óptica y Electrónica and the University of Massachusetts. The SMA is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics, and is funded by the Smithsonian Institution and the Academia Sinica. ALMA is a partnership of the European Southern Observatory (representing its member states), National Science Foundation (USA) and National Institutes of Natural Sciences (Japan), together with the National Research Council (Canada), Ministry of Science and Technology and Academia Sinica Institute of Astronomy and Astrophysics (Taiwan), and Korea Astronomy and Space Science Institute (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the European Southern Observatory, Associated Universities/National Radio Astronomy Observatory and National Astronomical Observatory of Japan.

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J.A.Z. led the scientific analysis and the writing of the paper, as well as the SMA follow-up proposal. R.J.I., E.V., S.E., A.C., H.D., J.S.D., L.D., M.J.M., S.S., M.W.L.S. and P.v.d.W. contributed to the original Herschel proposals and observations, by which this source was discovered and catalogued. A.M., D.H.H., E.V., I.A., V.A.-R., M.C., D.R.G., E.T. and O.V. performed the selection of the sample for the LMT observations and led the LMT proposals. M.S.Y., G.N., F.P.S., G.W.W., D.S.-A., A.V. and M.Z. carried out LMT data reduction and interpretation. D.W., M.S.Y. and A.I.G.-R. assisted with the SMA observations and data reduction. J.S., I.O. and H.N. contributed to the data analysis and fitting and modelling the results. All the authors discussed and contributed to the writing of the paper.

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Correspondence to Jorge A. Zavala.

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Zavala, J.A., Montaña, A., Hughes, D.H. et al. A dusty star-forming galaxy at z = 6 revealed by strong gravitational lensing. Nat Astron 2, 56–62 (2018). https://doi.org/10.1038/s41550-017-0297-8

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