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Astron. Astrophys. 358, 30-44 (2000)


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Detection of correlated galaxy ellipticities from CFHT data: first evidence for gravitational lensing by large-scale structures *

L. Van Waerbeke 1, Y. Mellier 2,3, T. Erben 4, J.C. Cuillandre 5, F. Bernardeau 6, R. Maoli 2,3, E. Bertin 2,3, H.J. Mc Cracken 7, O. Le Fèvre 7, B. Fort 2, M. Dantel-Fort 3, B. Jain 8 and P. Schneider 4

1 Canadian Institut for Theoretical Astrophysics, 60 St Georges Str., Toronto, M5S 3H8 Ontario, Canada
2 Institut d'Astrophysique de Paris, 98 bis, boulevard Arago, 75014 Paris, France
3 Observatoire de Paris, DEMIRM, 61, avenue de l'Observatoire, 75014 Paris, France
4 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, Postfach 1523, 85740 Garching, Germany
5 Canada-France-Hawaii-Telescope, P.O. Box 1597, Kamuela, Hawaii 96743, USA
6 Service de Physique Théorique, C.E. de Saclay, 91191 Gif sur Yvette Cedex, France
7 Laboratoire d'Astronomie Spatiale, 13376 Marseille Cedex 12, France
8 Department of Physics, Johns Hopkins University, Baltimore, MD 21218, USA

Received 1 March 2000 / Accepted 24 March 2000

Abstract

We report the detection of a significant (5.5 [FORMULA]) excess of correlations between galaxy ellipticities at scales ranging from 0.5 to 3.5 arc-minutes. This detection of a gravitational lensing signal by large-scale structure was made using a composite high quality imaging survey of 6300 arcmin2 obtained at the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic CCD cameras. The amplitude of the excess correlation is [FORMULA] at [FORMULA] scale, in agreement with theoretical predictions of the lensing effect induced by large-scale structure. We provide a quantitative analysis of systematics which could contribute to the signal and show that the net effect is small and can be corrected for. In particular, we show that the spurious excess of correlations caused by the residual of the anisotropic Point Spread Function (PSF) correction is well below the measured signal. We show that the measured ellipticity correlations behave as expected for a gravitational shear signal. The relatively small size of our survey precludes tight constraints on cosmological models. However the data are in favor of cluster normalized cosmological models, and marginally reject Cold Dark Matter models with ([FORMULA], [FORMULA]) or ([FORMULA], [FORMULA]). The detection of cosmic shear demonstrates the technical feasibility of using weak lensing surveys to measure dark matter clustering and the potential for cosmological parameter measurements, in particular with upcoming wide field CCD cameras.

Key words: cosmology: theory – cosmology: dark matter – cosmology: gravitational lensing – cosmology: large-scale structure of Universe

* Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada (NRCC), the Institut des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique (CNRS) and the University of Hawaii (UH)

Send offprint requests to: waerbeke@cita.utoronto.ca

© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000

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