Letter | Published:

A clumpy and anisotropic galaxy halo at redshift 1 from gravitational-arc tomography

Nature volume 554, pages 493496 (22 February 2018) | Download Citation


Every star-forming galaxy has a halo of metal-enriched gas that extends out to at least 100 kiloparsecs1,2,3, as revealed by the absorption lines that this gas imprints on the spectra of background quasars4. However, quasars are sparse and typically probe only one narrow beam of emission through the intervening galaxy. Close quasar pairs5,6,7 and gravitationally lensed quasars8,9,10,11 have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circumgalactic medium remains poorly constrained. As a result, our understanding of the physical processes that drive the recycling of baryons across the lifetime of a galaxy is limited12,13. Here we report integral-field (tomographic) spectroscopy of an extended background source—a bright, giant gravitational arc. We can thus coherently map the spatial and kinematic distribution of Mg ɪɪ absorption—a standard tracer of enriched gas—in an intervening galaxy system at redshift 0.98 (around 8 billion years ago). Our gravitational-arc tomography unveils a clumpy medium in which the absorption strength decreases with increasing distance from the galaxy system, in good agreement with results for quasars. Furthermore, we find strong evidence that the gas is not distributed isotropically. Interestingly, we detect little kinematic variation over a projected area of approximately 600 square kiloparsecs, with all line-of-sight velocities confined to within a few tens of kilometres per second of each other. These results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow.

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This work has benefitted from discussions with A. Smette, N. Nielsen and G. Kacprzak. S.L. thanks the European Southern Observatory Scientific Visitor Selection Committee for supporting a research stay at the ESO headquarters in Santiago, where part of this work was done. S.L. has been supported by FONDECYT grant number 1140838. This work has also been partially supported by PFB-06 CATA. N.T. acknowledges support from CONICYT PAI/82140055.

Author information


  1. Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

    • Sebastian Lopez
  2. Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile

    • Nicolas Tejos
  3. European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura 19, Santiago, Chile

    • Cédric Ledoux
  4. Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile

    • L. Felipe Barrientos
    •  & Ismael Pessa
  5. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109, USA

    • Keren Sharon
  6. Observational Cosmology Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA

    • Jane R. Rigby
  7. Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

    • Michael D. Gladders
  8. Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

    • Michael D. Gladders
  9. Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    • Matthew B. Bayliss


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S.L. conceived and led the project. S.L. and N.T. wrote the MUSE telescope-time proposal and designed the observations. L.F.B. and N.T. prepared the remote observations and L.F.B. reduced the MUSE data. S.L., N.T. and C.L. analysed the data, performed simulations and devised ways to produce and interpret the results. S.L. wrote the main codes. N.T. and I.P. performed the blind survey of galaxies in the field of view. K.S. performed the lens model and L.F.B. supervised the design of Fig. 1. M.B.B. and L.F.B. performed the photometric characterization of the absorbing galaxies, and S.L., C.L. and N.T. the analysis of their spectra. Ancillary data from MagE and HST were provided by J.R.R. and M.D.G. S.L. wrote the manuscript and produced the rest of the figures, with contribution from N.T. All co-authors provided critical feedback and helped to shape the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sebastian Lopez.

Reviewer Information Nature thanks H.-W. Chen and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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