The VIMOS VLT Deep Survey: The faint type-1 AGN sample

We present the type-1 active galactic nuclei (AGN) sample extracted from the VIMOS VLT Deep Survey's first observations of 21 000 spectra in 1.75 deg(2). This sample, which is purely magnitude-limited and free of morphological or color-selection biases, contains 130 broad-line AGN (BLAGN) spectra with redshift up to 5. Our data are divided into a wide (I-AB <= 22.5) and a deep (I-AB <= 24) subsample containing 56 and 74 objects, respectively. Because of its depth and selection criteria, this sample is uniquely suited for studying the population of faint type-1 AGN. Our measured surface density (similar to 472 +/- 48 BLAGN per square degree with I-AB <= 24) is significantly higher than that of any other optically selected sample of BLAGN with spectroscopic confirmation. By applying a morphological and color analysis to our AGN sample, we find that (1) similar to 23% of the AGN brighter than I-AB = 22.5 are classified as extended, and this percentage increases to similar to 42% for those with z < 1.6; (2) a non-negligible fraction of our BLAGN are lying close to the color-space area occupied by stars in the u(*) - g ' versus g ' - r ' color-color diagram. This leads us to the conclusion that the classical optical-ultraviolet preselection technique, if employed at such deep magnitudes (I-AB = 22.5) in conjuction with a preselection of point-like sources, can miss up to similar to 35% of the AGN population. Finally, we present a composite spectrum of our sample of objects. While the continuum shape is very similar to that of the SDSS composite at short wavelengths, it is much redder than that of the SDSS composite at. = 3000 angstrom. We interpret this as due to significant contamination from emission of the host galaxies, as expected from the faint absolute magnitudes sampled by our survey.