Letter

Nature 451, 541-544 (31 January 2008) | doi:10.1038/nature06555; Received 4 July 2007; Accepted 7 December 2007

A test of the nature of cosmic acceleration using galaxy redshift distortions

L. Guzzo1,2,3,4, M. Pierleoni3, B. Meneux5, E. Branchini6, O. Le Fèvre7, C. Marinoni8, B. Garilli5, J. Blaizot3, G. De Lucia3, A. Pollo7,9, H. J. McCracken10,11, D. Bottini5, V. Le Brun7, D. Maccagni5, J. P. Picat12, R. Scaramella13,14, M. Scodeggio5, L. Tresse7, G. Vettolani13, A. Zanichelli13, C. Adami7, S. Arnouts7, S. Bardelli15, M. Bolzonella15, A. Bongiorno16, A. Cappi15, S. Charlot10, P. Ciliegi15, T. Contini12, O. Cucciati1,17, S. de la Torre7, K. Dolag3, S. Foucaud18, P. Franzetti5, I. Gavignaud19, O. Ilbert20, A. Iovino1, F. Lamareille15, B. Marano16, A. Mazure7, P. Memeo5, R. Merighi15, L. Moscardini16,21, S. Paltani22,23, R. Pellò12, E. Perez-Montero12, L. Pozzetti15, M. Radovich24, D. Vergani5, G. Zamorani15 & E. Zucca15

  1. INAF–Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (LC), Italy
  2. Max Planck Institut für extraterrestrische Physik,
  3. Max Planck Institut für Astrophysik,
  4. European Southern Observatory, D-85748 Garching, Germany
  5. INAF–IASF, Via Bassini 15, I-20133, Milano, Italy
  6. Dipartimento di Fisica, Universitá Roma III, Via della Vasca Navale 84, I-00146 Roma, Italy
  7. Laboratoire d'Astrophysique de Marseille, UMR6110, CNRS-Université de Provence, BP8, F-13376 Marseille cedex 12, France
  8. Centre de Physique Theorique, UMR 6207 CNRS-Université de Provence, F-13288 Marseille, France
  9. The Andrzej Soltan Institute for Nuclear Research, Hoza 69, 00-681 Warsawa, Poland
  10. Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bvd Arago,
  11. Observatoire de Paris, LERMA, 61 Avenue de l'Observatoire, F-75014 Paris, France
  12. Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées (UMR 5572), 14 avenue E. Belin, F-31400 Toulouse, France
  13. INAF–IRA, Via Gobetti 101, I-40129 Bologna, Italy
  14. INAF–Osservatorio Astronomico di Roma, Via di Frascati 33, I-00040 Monte Porzio Catone, Italy
  15. INAF–Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
  16. Università di Bologna, Dipartimento di Astronomia, Via Ranzani 1, I-40127 Bologna, Italy
  17. Dipartimento di Fisica–Universitá di Milano-Bicocca, Piazza delle Scienze 3, I-20126 Milano, Italy
  18. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
  19. Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
  20. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
  21. INFN–Sezione di Bologna, viale Berti-Pichat 6/2, I-40127 Bologna, Italy
  22. Geneva Observatory, ch. des Maillettes 51, CH-1290 Sauverny, Switzerland
  23. Integral Science Data Centre, ch. d'Ecogia 16, CH-1290 Versoix, Switzerland
  24. INAF–Osservatorio Astronomico di Capodimonte, Via Moiariello 16 I-80131, Napoli, Italy

Correspondence to: L. Guzzo1,2,3,4 Correspondence and requests for materials should be addressed to L.G. (Email: luigi.guzzo@brera.inaf.it).

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion1, 2 the physical cause of which is a mystery3. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this 'dark energy' corresponds to a 'cosmological constant', perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions4, 5, 6, 7, 8. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time9. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys10. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies11, 12, we measure the anisotropy parameter beta = 0.70 plusminus 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 plusminus 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift.

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