THE ESO-SCULPTOR FAINT GALAXY REDSHIFT SURVEY - THE PHOTOMETRIC SAMPLE

We present the photometric sample of a faint galaxy survey carried out in the southern hemisphere, using CCD imaging at the 3.60 m and NTT-3 .5 m telescopes at La Silla (ESO). The survey area is a continuous str ip of 0.2 degrees x 1.53 degrees located at high galactic latitude (b( II) similar to -83 degrees) in the Sculptor constellation. The photome tric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. T o these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-co lour photometric catalog at this depth. This photometric survey also p rovides the entry catalog for a fully-sampled redshift survey of simil ar to 700 galaxies with R less than or equal to 20.5 (Bellanger et al. 1995a). In this paper, we describe the photometric observations and t he steps used in the data reduction. The analysis of objects and the s tar-galaxy separation with a neural network are performed using SExtra ctor, a new photometric software developed by E. Bertin (1996). By app lication of SExtractor to simulated frames and comparison of multiple measurements, we estimate that the photometric accuracy of our catalog is similar to 0.05(m) for R less than or equal to 22 Then, we use a m ethod to obtain a homogeneous photometric scale over the whole survey using the overlapping regions of neighbouring CCDs. The differential g alaxy number counts in B, V, R are in good agreement with previously p ublished CCD studies and confirm the evidence for significant evolutio n at faint magnitudes as compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The galaxy colour distributions B - R, B - V of our sample show a blueing trend of similar to 0.5(m) between 21 < R < 23.5 in contrast to the V - R colour distribution where no signific ant evolution is observed.