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We have obtained CCD photometry for 9500, 12150, 13000 galaxies in the B, V, R (Johnson-Cousins) filters to limiting magnitudes of 24.5, 24.0, 23.5 respectively over an area of 0.4 degtex2html_wrap_inline3357 near the southern galactic pole. Automatic procedures were designed in order to reduce the data in an homogeneous fashion. The main steps used in obtaining the photometric catalogue are summarized as follows:
i) We have applied the standard pre-reduction techniques of bias subtraction, flat-fielding by median filtering and cosmic-ray removal.
ii) Because different CCDs were used over the course of the programme, a large set of colour equations and zero-points were measured in order to provide reliable calibrations for the survey. We could then transform all instrumental magnitudes into the Johnson-Cousins standard system.
iii) The survey data is a mosaic of tex2html_wrap_inline3359 CCD frames in each band which have tex2html_wrap_inline3361 arcmin overlaps. We could therefore perform an internal and global re-adjustment of the zero-point of each CCD over the whole survey. In this way, we reduce the zero-point field-to-field scatter from tex2html_wrap_inline3363 mag to tex2html_wrap_inline3365 mag, in agreement with the photometric uncertainty estimated using simulated images (tex2html_wrap_inline3367 for tex2html_wrap_inline3369 and tex2html_wrap_inline3371 at fainter magnitudes). We therefore reduce the internal dispersion in our photometry to the intrinsic dispersion resulting from the limitations of the photometric package.
iv) Accurate astrometry is performed for each CCD frame. The positional accuracy is tex2html_wrap_inline3373 for objects with tex2html_wrap_inline3375 and increases to tex2html_wrap_inline3377 at fainter magnitudes, as estimated from objects located in the overlapping edges of the CCDs.
v) Measurement of the object colours is performed by matching the astronomical coordinates in each band with a tolerance of tex2html_wrap_inline3379 in position offset. The colour completeness with respect to the B band (fraction of B objects with R and V counterparts) is greater than 95% up to tex2html_wrap_inline3389 and drops to 60% at 24.5. The colour uncertainties are estimated as the corresponding quadratic sum of the errors in the photometric magnitudes (tex2html_wrap_inline3391 for tex2html_wrap_inline3393 and tex2html_wrap_inline3395 for tex2html_wrap_inline3397).
vi) The star-galaxy separation is performed using a neural network and is expected to be close to a 95% success rate for tex2html_wrap_inline3399. We use the R band for the star/galaxy separation because it is our deeper band, it was observed with the best seeing conditions, and it is used for the spectroscopic selection. At tex2html_wrap_inline3403, no separation is done due to the small fraction of faint stars expected (tex2html_wrap_inline3405) at the high galactic latitude of the survey (tex2html_wrap_inline3407).

The first results from the large photometric catalogue show that:
i) The galaxy counts in apparent magnitude and their slopes in logarithmic scale are in good agreement with previous CCD and photographic surveys and show an excess in all 3 bands with respect to the non-evolving models.
ii) The (B-V) and (B-R) median galaxy colours show a blueing shift of tex2html_wrap_inline3413 mag from tex2html_wrap_inline3415 to tex2html_wrap_inline3417. In contrast, the (V-R) median colour is nearly constant up to tex2html_wrap_inline3421.
iii) The galaxy counts are well fitted by a non-evolving model for tex2html_wrap_inline3423. using a tex2html_wrap_inline3425 derived from the new bright galaxy counts of Bertin & Dennefeld (1997).
iv) Two peaks in the stellar distributions are present in good agreement with the Robin & Crézé (1986) model of the galactic disk and halo.
The next step in the study of this photometric sample is the analysis of the angular correlation function tex2html_wrap_inline3427 at faint magnitude (Arnouts & de Lapparent 1997). This work will provide information about the galaxy clustering ever a wide range of scales and apparent magnitudes. The high completeness rate in colour should also allow to further characterize the properties of the faint blue galaxies.
Together with the photometric data, the redshift survey of tex2html_wrap_inline3429 galaxies with tex2html_wrap_inline3431 will provide a multi-colour optical luminosity function in the redshift range tex2html_wrap_inline3433. Altogether, these data will allow us to address the issue of the evolution of galaxies with tex2html_wrap_inline3435. The photometric and redshift catalogues will also be complemented by a spectral classification of all galaxies with tex2html_wrap_inline3437 (Galaz & de Lapparent 1996) and will thus provide an unique database for studying the variations in the galaxy properties as a fonction of environment and redshift.


We are grateful to the European Southern Observatory for the large amount of observing time and the corresponding logistic support which allowed to perform this observing programme in good conditions and to bring it to completion. We are grateful to Dr. P. Leisy for kindly providing us his cosmic removal algorithm, and to M. Fioc and Dr. B. Rocca-Volmerange for kindly providing us the non-evolving model to fit the differential galaxy number counts. We thank Dr. C. Willmer for fruitful discussions. We also thank the referee Dr. N. Metcalfe for his scientific comments and linguistic corrections.

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