The VIMOS VLT deep survey -: First epoch VVDS-deep survey:: 11564 spectra with 17.5≤IAB≤24, and the redshift distribution over 0≤z≤5

This paper presents the "First Epoch" sample from the VIMOS VLT Deep Survey (VVDS). The VVDS goals, observations, data reduction with the VIPGI pipeline and redshift measurement scheme with KBRED are discussed. Data have been obtained with the VIsible Multi Object Spectrograph ( VIMOS) on the ESO-VLT UT3, allowing us to observe similar or equal to 600 slits simultaneously at a spectral resolution R similar or equal to 230. A total of 11 564 objects have been observed in the VVDS-02h and VVDS-CDFS "Deep" fields over a total area of 0.61 deg(2), selected solely on the basis of apparent magnitude 17.5 <= I-AB <= 24. The VVDS efficiently covers the redshift range 0 < z <= 5. It is successfully going through the "redshift desert" 1.5 < z < 2.2, while the range 2.2 < z < 2.7 remains of difficult access because of the VVDS wavelength coverage. A total of 9677 galaxies have a redshift measurement, 836 objects are stars, 90 objects are AGN, and a redshift could not be measured for 961 objects. There are 1065 galaxies with a measured redshift z >= 1.4. When considering only the primary spectroscopic targets, the survey reaches a redshift measurement completeness of 78% overall ( 93% including less reliable flag 1 objects), with a spatial sampling of the population of galaxies of similar to 25% and similar to 30% in the VVDS-02h and VVDS-CDFS respectively. The redshift accuracy measured from repeated observations with VIMOS and comparison to other surveys is similar to 276 km s(-1). From this sample we are able to present for the first time the redshift distribution of a magnitude-limited spectroscopic sample down to I-AB <= 24. The redshift distribution N(z) has a median of z = 0.62, z = 0.65, z = 0.70, and z = 0.76, for magnitude-limited samples with IAB = 22.5, 23.0, 23.5 and 24.0 respectively. A high redshift tail above redshift 2 and up to redshift 5 becomes readily apparent for I-AB > 23.5, probing the bright star-forming population of galaxies. This sample provides an unprecedented dataset to study galaxy evolution over similar to 90% of the life of the universe.