The VIRMOS deep imaging survey -: I.: Overview, survey strategy, and CFH12K observations

This paper describes the CFH12K-VIRMOS survey: a deep BVRI imaging survey in four fields totalling more than 17 deg(2), conducted with the 40x30 arcmin(2) field CFH-12K camera. The survey is intended to be a multi-purpose survey used for a variety of science goals, including surveys of very high redshift galaxies and weak lensing studies. Four high galactic latitude fields, each 2 x 2 deg(2), have been selected along the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg(2) of the "wide" survey are covered with exposure times of 2 hr, 1.5 hr, 1 hr, 1 hr, respectively while the 1.3x1 deg(2) area of the "deep" survey at the center of the 0226-04 field is covered with exposure times of 7 h, 4.5 h, 3 h, 3 h, in BVRI respectively. An additional area similar to2 deg(2) has been imaged in the 0226-04 field corresponding to the area surveyed by the XMM-LSS program (Pierre et al. 2003). The data is pipeline processed at the Terapix facility at the Institut d'Astrophysique de Paris to produce large mosaic images. The catalogs produced contain the positions, shapes, total and aperture magnitudes for 2.175 million objects measured in the four areas. The limiting magnitudes, measured as a 5sigma measurement in a 3 arcsec diameter aperture is I-AB=24.8 in the "Wide" areas, and I-AB=25.3 in the deep area. Careful quality control has been applied on the data to ensure internal consistency and assess the photometric and astrometric accuracy as described in a joint paper (McCracken et al. 2003). These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a large spectroscopic survey of the distant universe (Le Fevre et al. 2003). First results from the CFH12K-VIRMOS survey have been published on weak lensing (e.g. van Waerbeke & Mellier 2003). Catalogs and images are available through the VIRMOS database environment under Oracle (http://www.oamp.fr/cencos). They are open for general use since July 1st, 2003.