Observational Cosmology 3 from Friedmann expansion, then such modifications are strongly constrained at early times, at energies on the order of 1 MeV. In the local Universe, most galaxies are dominated by stars, with less than ten per cent of their visible mass in the form of gas. Determining when most of these stars formed is one of the central issues of observational cosmology. Optical and ultraviolet observations of high-redshift galaxies (particularly those in the Hubble Deep Field) have been interpreted as indicating that the peak of star formation occurred between redshifts of 1 and 1.5. But it is known that star formation takes place in dense clouds, and is often hidden at optical wavelengths because of extinction by dust in the clouds. Here we report a deep submillimetre-wavelength survey of the Hubble Deep Field; these wavelengths trace directly the emission from dust that has been warmed by massive star-formation activity. Ata chapters and subchapters pdf converter. The combined radiation of the five most significant detections accounts for 30–50 per cent of the previously unresolved background emission in this area. Four of these sources appear to be galaxies in the redshift range 2. Affiliations • *Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK • David H. Hughes •, James Dunlop •, Rob Ivison •, John Peacock • & Andy Lawrence • †Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BZ, UK • Stephen Serjeant •, Michael Rowan-Robinson •, Robert G. Mann •, Andreas Efstathiou •, Seb Oliver • & Pippa Goldschmidt • ‡Cavendish Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK • Andrew Blain • & Malcolm Longair • §Mullard Space Science Laboratory, University College London, Holmbury St Mary, Surrey RH5 6NT, UK • Walter Gear • ‖Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, Hawaii 96720, USA • Tim Jenness. Authors • Search for David H. Hughes in: • • • • • • Search for Stephen Serjeant in: • • • • • • Search for James Dunlop in: • • • • • • Search for Michael Rowan-Robinson in: • • • • • • Search for Andrew Blain in: • • • • • • Search for Robert G. Mann in: • • • • • • Search for Rob Ivison in: • • • • • • Search for John Peacock in: • • • • • • Search for Andreas Efstathiou in: • • • • • • Search for Walter Gear in: • • • • • • Search for Seb Oliver in: • • • • • • Search for Andy Lawrence in: • • • • • • Search for Malcolm Longair in: • • • • • • Search for Pippa Goldschmidt in: • • • • • • Search for Tim Jenness in: • • • • • Corresponding author Correspondence to.
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