Letter | Published:

Galaxies at redshifts 5 to 6 with systematically low dust content and high [C ii] emission

Nature volume 522, pages 455458 (25 June 2015) | Download Citation


The rest-frame ultraviolet properties of galaxies during the first three billion years of cosmic time (redshift z > 4) indicate a rapid evolution in the dust obscuration of such galaxies1,2,3. This evolution implies a change in the average properties of the interstellar medium, but the measurements are systematically uncertain owing to untested assumptions4,5 and the inability to detect heavily obscured regions of the galaxies. Previous attempts to measure the interstellar medium directly in normal galaxies at these redshifts have failed for a number of reasons6,7,8,9, with two notable exceptions10,11. Here we report measurements of the forbidden C ii emission (that is, [C ii]) from gas, and the far-infrared emission from dust, in nine typical star-forming galaxies about one billion years after the Big Bang (z ≈ 5–6). We find that these galaxies have thermal emission that is less than 1/12 that of similar systems about two billion years later, and enhanced [C ii] emission relative to the far-infrared continuum, confirming a strong evolution in the properties of the interstellar medium in the early Universe. The gas is distributed over scales of one to eight kiloparsecs, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z < 3 and being comparable in dust content to local low-metallicity systems12.

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Support for this work was provided by NASA through an award issued by JPL/Caltech. We thank the ALMA staff for facilitating the observations and aiding in the calibration and reduction process. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work is based in part on observations made with the Spitzer Space Telescope and the W.M. Keck Observatory, along with archival data from the NASA/ESA Hubble Space Telescope, the Subaru Telescope, the Canada-France-Hawaii-Telescope and the ESO Vista telescope obtained from the NASA/IPAC Infrared Science Archive. V.S. acknowledges funding by the European Union’s Seventh Framework programme under grant agreement 337595 (ERC Starting Grant, ‘CoSMass’).

Author information


  1. Infrared Processing and Analysis Center (IPAC), 1200 East California Boulevard, Pasadena, California 91125, USA

    • P. L. Capak
    •  & L. Yan
  2. California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA

    • P. L. Capak
    • , N. Scoville
    •  & L. Yan
  3. National Radio Astronomy Observatory, PO Box 0, Socorro, New Mexico 87801, USA

    • C. Carilli
  4. Astrophysics Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK

    • C. Carilli
  5. New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA

    • G. Jones
  6. Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, Texas 78712, USA

    • C. M. Casey
  7. Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, New York 14853, USA

    • D. Riechers
  8. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903, USA

    • K. Sheth
    •  & S. Lilly
  9. Institute for Astronomy, ETH Zurich, CH-8093 Zurich, Switzerland

    • C. M. Carollo
  10. Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France

    • O. Ilbert
    •  & O. LeFevre
  11. Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn, Germany

    • A. Karim
  12. Physics Department, University of Zagreb, Bijenička cesta 32, 10002 Zagreb, Croatia

    • V. Smolcic


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P.L.C. proposed and carried out the observations, conducted the analysis in this paper, and authored the majority of the text. C.C., G.J. and K.S. carried out the reduction and direct analysis of the ALMA data. C.M.C. consulted on the spectral energy distribution fitting and interpretation of the data, and also conducted a blind test of the FIR luminosity, [C ii] line luminosity, and β measurements, along with testing for sample selection effects. D.R. conducted the spectral line analysis and carried out an independent blind check of the ALMA data reduction. O.I. carried out the spectral energy distribution fitting and consulted on their interpretation. C.M.C., A.K., O.L., S.L., N.S., V.S. and L.Y. contributed to the overall interpretation of the results and various aspects of the analysis.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to P. L. Capak.

This paper makes use of ALMA data: ADS/JAO.ALMA#2012.1.00523.S. ALMA.

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