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 $0.2^{\circ} \times 1.53^{\circ}$ located at high galactic latitude ($b^{II} \sim -83^{\circ}$) 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 ~ 700 galaxies with $R\le 20.5$ (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 $\sim 0.05^{\rm m}$ for $R \le 22$. 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 $\sim 0.5^{\rm m}$ between $21 < R < 23.5$ in contrast to the $V-R$ colour distribution where no significant evolution is observed