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 strip of 0.2 degrees x 1.53 degrees located at high galactic latitude (b(II) similar to -83 degrees) in the Sculptor constellation. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey also provides the entry catalog for a fully-sampled redshift survey of similar 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 the steps used in the data reduction. The analysis of objects and the star-galaxy separation with a neural network are performed using SExtractor, a new photometric software developed by E. Bertin (1996). By application 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 method to obtain a homogeneous photometric scale over the whole survey using the overlapping regions of neighbouring CCDs. The differential galaxy number counts in B, V, R are in good agreement with previously published CCD studies and confirm the evidence for significant evolution 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 significant evolution is observed.