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

2012; Nature Portfolio; Volume: 486; Issue: 7402 Linguagem: Inglês

10.1038/nature11073

1476-4687

Fabian Walter, Roberto Decarli, C. L. Carilli, F. Bertoldi, P. Cox, Elisabete da Cunha, E. Daddi, Mark Dickinson, Dennis Downes, D. Elbaz, Richard S. Ellis, Jacqueline Hodge, R. Neri, Dominik A. Riechers, A. Weiß, Eric F. Bell, H. Dannerbauer, Melanie Krips, Mark R. Krumholz, L. Lentati, R. Maiolino, K. M. Menten, Hans‐Walter Rix, Brant Robertson, Hyron Spinrad, Dan Stark, Daniel Stern,

Astrophysics and Cosmic Phenomena

Using a millimetre-wave molecular line scan, a redshift has finally been determined for the extremely active star-forming galaxy HDF 850.1 in the Hubble Deep Field, which makes it younger than thought at 1.1 billion years after the Big Bang. The brightest sub-millimetre radio source in the Hubble Deep Field view of the distant Universe, known as HDF 850.1, has proved enigmatic, evading detection in the optical and near-infrared ranges despite an intensive search. Without the discovery of a counterpart at shorter wavelengths, it has not been possible to estimate the source's redshift, size or mass directly. Now, by using a millimetre-wave molecular line scan, the redshift of HDF 850.1 has been determined. At z ≈ 5.2, it is much higher than expected and corresponds to a cosmic age of only 1.1 billion years after the Big Bang. Calculations from the new data suggest a high annual star formation rate of 850 solar masses and a mass of 1.3 × 1011 solar masses. But as yet there is no sign of a starlight-emitting counterpart. 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.