The VIRMOS deep imaging survey: III. ESO/WFI deep U-band imaging of the 0226-04 deep field

In this paper we describe the U-band imaging of the F02 deep field, one of the fields in the VIRMOS Deep Imaging Survey. The observations were done at the ESO/MPG 2.2m telescope at La Silla (Chile) using the 8k x 8k Wide-Field Imager (WFI). The field is centered at alpha(J2000)=02h 26m 00s and delta(J2000)=-04deg 30' 00", the total covered area is 0.9 deg**2 and the limiting magnitude (50% completeness) is U(AB) ~ 25.4 mag. Reduction steps, including astrometry, photometry and catalogue extraction, are first discussed. The achieved astrometric accuracy (RMS) is ~ 0.2" with reference to the I-band catalog and ~ 0.07" internally (estimated from overlapping sources in different exposures). The photometric accuracy including uncertainties from photometric calibration, is < 0.1 mag. Various tests are then performed as a quality assessment of the data. They include: (i) the color distribution of stars and galaxies in the field, done together with the BVRI data available from the VIMOS survey; (ii) the comparison with previous published results of U-band magnitude-number counts of galaxies.