Publication : t00/031

Abstract:
We report the detection of a significant (5.5 $\sigma$) excess of correlation 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 $6300$ arcmin$^2$ obtained at the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic CCD cameras. The amplitude of the excess correlation is $2.4\%,$ in agreement with the 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 correlation caused by the residual of the anisotropic Point Spread Function (PSF) correction is well below the measured signal. We show that the ellipticity correlation signal behaves as the predictions given by the gravitational lensing theory. The relatively small size of our survey precludes tight constraints on cosmological models, although the data are in agreement with cluster normalized models, and marginally reject cold dark matter models with ($\Omega=0.3$, $\sigma_8<0.6$) or ($\Omega=1$, $\sigma_8=1$). 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.