A search for edge-on galaxy lenses in the CFHT Legacy Survey

Context. The new generation of wide-field optical imaging as the Canada France Hawaii Telescope Legacy Survey (CFHTLS) enables discoveries of all types of gravitational lenses present in the sky. The Strong Lensing Legacy Survey (SL2S) project has started an inventory of clusters or groups of galaxies lenses and of Einstein rings around distant massive ellipticals. Aims. Here we attempt to extend this inventory by finding lensing events produced by massive edge-on disk galaxies that remain a poorly documented class of lenses. Methods. We implemented and tested an automated search procedure of edge-on galaxy lenses in the CFHTLS Wide fields with magnitude 18 < i < 21, inclination angle lower than 25 ◦ , and a photometric redshift determination. This procedure estimated the lensing convergence of each galaxy from the Tully-Fisher law and selected only those few candidates that exhibit a possibly nearby arc configuration at a radius compatible with this convergence (rarc 2rE). The efficiency of the procedure was tested after a visual examination of the whole initial sample of 30 444 individual edge-on disks. Results. After calculating the surface density of edge-on lenses possibly detected in a survey for a given seeing, we deduce that this theoretical number is about 10 for the CFHTLS Wide, a number in broad agreement with the 2 good candidates detected here. We show that the Tully-Fisher selection method is very efficient at finding valuable candidates, though its accuracy depends on the quality of the photometric redshift of the lenses. Finally, we argue that future surveys will detect at least a hundred of such lens candidates.