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Nature 410, 169-173 (8 March 2001) | doi:10.1038/35065528; Received 20 December 2000; Accepted 30 January 2001

A measurement of the cosmological mass density from clustering in the 2dF Galaxy Redshift Survey

John A. Peacock1, Shaun Cole2, Peder Norberg2, Carlton M. Baugh2, Joss Bland-Hawthorn3, Terry Bridges3, Russell D. Cannon3, Matthew Colless4, Chris Collins5, Warrick Couch6, Gavin Dalton7, Kathryn Deeley6, Roberto De Propris6, Simon P. Driver8, George Efstathiou9, Richard S. Ellis9,10, Carlos S. Frenk2, Karl Glazebrook11, Carole Jackson4, Ofer Lahav9, Ian Lewis3, Stuart Lumsden12, Steve Maddox13, Will J. Percival1, Bruce A. Peterson4, Ian Price4, Will Sutherland1,7 & Keith Taylor3,10

  1. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
  2. Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
  3. Anglo-Australian Observatory, P.O. Box 296, Epping, New South Wales 2121, Australia
  4. Research School of Astronomy & Astrophysics, The Australian National University, Weston Creek, ACT 2611, Australia
  5. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead L14 1LD, UK
  6. Department of Astrophysics, University of New South Wales, Sydney, New South Wales 2052, Australia
  7. Department of Physics, University of Oxford, Keble Road, Oxford OX3RH, UK
  8. School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY6 9SS, UK
  9. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
  10. Department of Astronomy, Caltech, Pasadena, California 91125, USA
  11. Department of Physics & Astronomy, Johns Hopkins University, Baltimore, Maryland 21218-2686, USA
  12. Department of Physics, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
  13. School of Physics & Astronomy, University of Nottingham, Nottingham NG7 2RD, UK

Correspondence to: John A. Peacock1 Correspondence and requests for materials should be addressed to J.A.P. (e-mail: Email: jap@roe.ac.uk).

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The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter beta = Omega0.6/b = 0.43 plusminus 0.07, where Omega is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with Omega approximately 0.3.