Abstract. We report a measurement of cosmic shear correlations using an effective area of 6.5 deg 2 of the VIRMOS deep imaging survey in progress at the Canada-France-Hawaii Telescope. We measured various shear correlation functions, the aperture mass statistic and the top-hat smoothed variance of the shear with a detection significance exceeding 12 σ. We present results on angular scales from 3 arcsec to half a degree. The lensing origin of the signal is confirmed through tests that rely on the scalar nature of the gravitational potential. The different statistical measures give consistent results over the full range of angular scales. These important tests of the measurements demonstrate that the measured correlations could provide accurate constraints on cosmological parameters, subject to the systematic uncertainty in the source redshift distribution. The measurement over more than two decades of scale allows one to evaluate the effect of the shape of the power spectrum on cosmological parameter estimation. The degeneracy on σ8 − Ω0 can be broken if priors on the shape of the linear power spectrum (parameterized by Γ) are assumed. For instance, with Γ = 0.21 and at the 95% confidence level, we obtain 0.65 < σ8 < 1.2 and 0.22 < Ω0 < 0.55 for open models, and σ8 > 0.7 and Ω0 < 0.4 for flat (Λ-CDM) models. We discuss how these results would scale if the assumed source redshift distribution needed to be modified with forthcoming measurements of photometric redshifts. From the tangential/radial mode decomposition we can set an upper limit on the intrinsic shape alignment, which has recently been suggested as a possible contribution to the lensing signal. Within the error bars, there is no detection of intrinsic shape alignment for scales larger than 1 .

Abstract. In this paper we describe in detail the reduction, preparation and reliability of the photometric catalogues which comprise the CFH12K-VIRMOS deep field. This region, consisting of four contiguous pointings of the CFH12K wide-field mosaic camera, covers a total area of 1.2 deg 2 . The survey reaches a limiting magnitude of B AB ∼ 26.5, V AB ∼ 26.2, R AB ∼ 25.9 and I AB ∼ 25.0 (corresponding to the point at which our recovery rate for simulated point-like sources sources falls below 50%). In total the survey contains 90 729 extended sources in the magnitude range 18.0 < I AB < 24.0. We demonstrate our catalogues are free from systematic biases and are complete and reliable down these limits. By comparing our galaxy number counts to previous wide-field CCD surveys, we estimate that the upper limit on bin-to-bin systematic photometric errors for the I− limited sample is ∼10% in this magnitude range. We estimate that 68% of the catalogues sources have absolute per co-ordinate astrometric uncertainties less than |∆α| ∼ 0.38 and |∆δ| ∼ 0.32 . Our internal (filter-to-filter) per co-ordinate astrometric uncertainties are |∆α| ∼ 0.08 and |∆δ| ∼ 0.08 . We quantify the completeness of our survey in the joint space defined by object total magnitude and peak surface brightness. We also demonstrate that no significant positional incompleteness effects are present in our catalogues to I AB < 24.0. Finally, we present numerous comparisons between our catalogues and published literature data: galaxy and star counts, galaxy and stellar colours, and the clustering of both point-like and extended populations. In all cases our measurements are in excellent agreement with literature data to I AB < 24.0. This combination of depth and areal coverage makes this multi-colour catalogue a solid foundation to select galaxies for follow-up spectroscopy with VIMOS on the ESO-VLT and a unique database to study the formation and evolution of the faint galaxy population to z ∼ 1 and beyond.

Aims. We present data from the CFHTLS Strong Lensing Legacy Survey (SL2S). Due to the unsurpassed combined depth, area and image quality of the Canada-France-Hawaii Legacy Survey it is becoming possible to uncover a large, statistically well-defined sample of strong gravitational lenses which spans the dark halo mass spectrum predicted by the concordance model from galaxy to cluster haloes. Methods. We describe the development of several automated procedures to find strong lenses of various mass regimes in CFHTLS images.Results. The preliminary sample of about 40 strong lensing candidates discovered in the CFHTLS T0002 release, covering an effective field of view of 28 deg 2 is presented. These strong lensing systems were discovered using an automated search and consist mainly of gravitational arc systems with splitting angles between 2 and 15 arcsec. This sample shows for the first time that it is possible to uncover a large population of strong lenses from galaxy groups with typical halo masses of about 10 13 h −1 M . We discuss the future evolution of the SL2S project and its main scientific aims for the next 3 years, in particular our observational strategy to extract the hundreds of gravitational rings also present in these fields.