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 β = 0.70 ± 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 ± 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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L.G. thanks M. Longair, C. Baugh, C. Porciani, P. Norberg, J. Peacock, A. Szalay and Y. Wang for discussions, S. White for suggestions and encouragement and L. Amendola, C. Di Porto and E. Linder for providing model predictions in electronic form. G. Pratt, S. White and E. Linder are gratefully acknowledged for reading the manuscript. L.G. acknowledges the support and hospitality of MPE, MPA and the European Southern Observatory (ESO) during this work. This research has been developed within the framework of the VVDS consortium and has been partially supported by the CNRS-INSU and its Programme National de Cosmologie (France), and by PRIN-INAF 2005. The VLT-VIMOS observations were carried out on guaranteed time allocated by the ESO to the VIRMOS consortium, under a contractual agreement between the CNRS of France, heading a consortium of French and Italian institutes, and the ESO, to design, manufacture and test the VIMOS instrument.
Author Contributions All authors worked on the preparation, observation, reduction and measurement of the spectroscopic data using codes developed by B.G., D.B., R.S., M.S., P.F., S.P. and A.Z. Spectroscopy was based on imaging data procured and processed by H.J.McC., S.F., O.L.F., M.R. and A.I. and organized in a database by V.L.B. and L.T. L.G., B.M., A.P., O.L.F., S.d.l.T. and M.P. developed the codes to measure galaxy correlations. M.P., E.B., L.G., C.M., L.M. and K.D. modelled the measurements and performed the Monte Carlo tests. J.B. and G.D.L. built the mock samples that were processed to mimic the VVDS by B.M., B.G. and P.M. This paper is dedicated to P. Schuecker.
The file contains Supplementary Notes with additional references and Supplementary Figures 1-2 with Legends.
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Monthly Notices of the Royal Astronomical Society (2019)