The CFHTLS strong lensing legacy survey

I. Survey overview and T0002 release sample

¹ Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Hw., Kamuela, Hawaii 96743, USA e-mail: cabanac@cfht.hawaii.edu
² Observatoire de Paris, LERMA, CNRS-UMR8112, 61 avenue de l'Observatoire, 75014 Paris, France
³ Institut d'Astrophysique de Paris, CNRS-UMR7095 and Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁴ Laboratoire d'Astrophysique de Toulouse-Tarbes, CNRS-UMR5572 and Université Paul Sabatier Toulouse III, 14 avenue Édouard Belin, 31400 Toulouse, France
⁵ 
Gemini Observatory Northern Operations Center, 670 N. A'ohoku Place, Hilo, Hawaii 96720, USA
⁶ Laboratoire d'Astrophysique de Marseille, traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France
⁷ Observatoire de Paris, GEPI, CNRS-UMR8111, 5 place Jules Janssen, 92195 Meudon Cedex, France

Received: 12 June 2006
Accepted: 5 September 2006

Abstract

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 deg² 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 . 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.