Intense star formation within resolved compact regions in a galaxy at z = 2.3

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Massive galaxies in the early Universe have been shown to be forming stars at surprisingly high rates1,2,3. Prominent examples are dust-obscured galaxies which are luminous when observed at sub-millimetre wavelengths and which may be forming stars at a rate of 1,000 solar masses (M) per year4,5,6,7. These intense bursts of star formation are believed to be driven by mergers between gas-rich galaxies8,9. Probing the properties of individual star-forming regions within these galaxies, however, is beyond the spatial resolution and sensitivity of even the largest telescopes at present. Here we report observations of the sub-millimetre galaxy SMMJ2135-0102 at redshift z = 2.3259, which has been gravitationally magnified by a factor of 32 by a massive foreground galaxy cluster lens. This magnification, when combined with high-resolution sub-millimetre imaging, resolves the star-forming regions at a linear scale of only 100 parsecs. We find that the luminosity densities of these star-forming regions are comparable to the dense cores of giant molecular clouds in the local Universe, but they are about a hundred times larger and 107 times more luminous. Although vigorously star-forming, the underlying physics of the star-formation processes at z ≈ 2 appears to be similar to that seen in local galaxies, although the energetics are unlike anything found in the present-day Universe.

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Figure 1: Multi-wavelength images of the galaxy cluster MACSJ2135-0102.
Figure 2: Carbon monoxide observations of SMMJ2135-0102 obtained with the Green Bank Telescope and Plateau de Bure Interferometer.
Figure 3: Spectral energy distribution of the lensed galaxy.
Figure 4: Relation between size and luminosity of star forming regions.


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We thank the staff at Green Bank Telescope for scheduling the Zpectrometer observations at short notice, and the ESO director for granting director’s discretionary time observations with SABOCA. A.M.S. gratefully acknowledges a Royal Astronomical Society Sir Norman Lockyer Fellowship, and J.R. and D.P.S. acknowledge a Marie Curie fellowship and a Science Technology and Facilities Council fellowship respectively. J.D.Y. acknowledges support from NASA through a Hubble Fellowship. The Zpectrometer observations were carried out on the Robert C. Byrd Green Bank Telescope, which is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The APEX observations were carried out with ESO Telescopes. The 870 μm interferometric observations were carried out with the Sub-Millimeter Array, which 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. The CO(3-2) observations were carried out with the Plateau de Bure Interferometer, which is supported by INSU/CNRS (France), Max Planck Gesellschaft (MPG; Germany), and Instituto Geográfico Nacional (IGN; Spain). J. D. Y. is a Hubble Fellow.

Author Contributions A.M.S., I.S., R.J.I. and A.C.E. designed and proposed the observations, collected the data and performed the multi-wavelength analysis. A.I.H., A.J.B. and L.J.H. conducted the Green Bank Telescope/Zpectrometer observations and reduced and analysed the data. C.D.B, A.L. and G.S. carried out the LABOCA and SABOCA observations and wrote a data-reduction pipeline. B.S. proposed and reduced the mid-infrared Spitzer observations. K.E.K.C. carried out the far-infrared spectral energy distribution fitting. S.L., R.B., M.G., D.W. and J.D.Y. conducted the Sub-Millimeter Array observations and reduced the data. P.C., M.K. and R.N carried out the Plateau de Bure Interferometer observations and reduced the data. J.R. constructed the gravitational lensing model. D.P.S. carried out the optical/near-infrared spectral energy distribution modelling. All co-authors discussed the results and commented on the manuscript.

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Correspondence to A. M. Swinbank.

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Supplementary Information

This file contains (1) Observations and Data Reduction; (2) Gravitational Lens Modelling; (3) Spectral Energy Distribution Analysis; (4) Size and Luminosity of Star-forming Regions; and Additional References. (PDF 257 kb)

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