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

## Abstract

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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## Acknowledgements

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.

## Author information

Authors

### Contributions

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.

### Corresponding author

Correspondence to Jorge A. Zavala.

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The authors declare no competing financial interests.

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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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