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The Hubble Deep Field provides one of the deepest multiwave-length views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time (1). 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 mass (3-7). 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 estimates (3,4,6,8) 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 X 10 (11) 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., We have obtained a full-frequency scan of the 3-mm band towards the Hubble Deep Field using the IRAM (Institut de Radioastronomie Millinietrique) Plateau de Bure Interferometer. The observations covered the [...]

The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z = 6.42, when the Universe was less than a billion years old) has an infrared luminosity of 2.2 x [10.sup.13] times that of the Sun (1,2), presumably significantly powered by a massive burst of star formation (3-6). In local examples of extremely luminous galaxies, such as Arp 220, the burst of star formation is concentrated in a relatively small central region of < 100 pc radius (7,8). It is not known on which scales stars are forming in active galaxies in the early Universe, at a time when they are probably undergoing their initial burst of star formation. We do know that at some early time, structures comparable to the spheroidal bulge of the Milky Way must have formed. Here we report a spatially resolved image of [C II] emission of the host galaxy of J114816.64+525150.3 that demonstrates that its star-forming gas is distributed over a radius of about 750 pc around the centre. The surface density of the star formation rate averaged over this region is ~1,000M [??] [year.sup.-1] [kpc.sup.-2]. This surface density is comparable to the peak in Arp 220, although about two orders of magnitude larger in area. This vigorous star-forming event is likely to give rise to a massive spheroidal component in this system., The forbidden ²[P.sub.3/2 → ²[P.sub.1/2] fine-structure line of ionized carbon ([C II]) at 158 µm provides effective cooling in regions where atomic transitions cannot be excited, and therefore helps gas [...]

Author(s): Fabian Walter (corresponding author) [1]; Frank Bertoldi [2]; Chris Carilli [1]; Pierre Cox [3]; K. Y. Lo [1]; Roberto Neri [4]; Xiaohui Fan [5]; Alain Omont [6]; Michael A. [...]