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The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field


The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time1. An early map of the Hubble Deep Field at a wavelength of 850 micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF 850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass3,4,5,6,7. Here we report a redshift of z = 5.183 for HDF 850.1, from a millimetre-wave molecular line scan. This places HDF 850.1 in a galaxy overdensity at z ≈ 5.2, corresponding to a cosmic age of only 1.1 billion years after the Big Bang. This redshift is significantly higher than earlier estimates3,4,6,8 and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3 × 1011 solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.

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Figure 1: Detection of four lines tracing the star-forming interstellar medium in HDF 850.1.
Figure 2: [C  ii ] line emission towards HDF 850.1.
Figure 3: Distribution of galaxies near HDF 850.1.

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This work is based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by MPG (Germany), INSU/CNRS (France) and IGN (Spain). The Jansky Very Large Array of NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. D.A.R. acknowledges support from NASA through a Spitzer Space Telescope grant. R.D. acknowledges funding through DLR project FKZ 50OR1004.

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F.W. had the overall lead of the project. The Plateau de Bure Interferometer data were analysed by R.D., F.W., P.C., R.N., M.K. and D.D. The Jansky Very Large Array data reduction was performed by C.C., J.H. and L.L. The molecular gas excitation was led by A.W. Spectroscopic redshift information was provided by M.D., R.E., H.S., D.S. and D.P.S. The spectral energy distribution analysis, including new Herschel data, was led by E.D.C, D.E. and E.D. An updated lensing model was provided by D.D. All authors helped with the proposal, data analysis and interpretation.

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Correspondence to Fabian Walter.

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The authors declare no competing financial interests.

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Walter, F., Decarli, R., Carilli, C. et al. The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field. Nature 486, 233–236 (2012).

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