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

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: igavignaud@aip.de
² Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées (UMR 5572), 14 avenue E. Belin, 31400 Toulouse, France
³ Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
⁴ Integral Science Data Centre, Ch. d'Écogia 16, 1290 Versoix
⁵ Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny
⁶ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ Laboratoire d'Astrophysique de Marseille – UMR 6110 CNRS, Université de Provence, BP 8, 13376 Marseille Cedex 12, France
⁹ IASF – INAF, via Bassini 15, 20133 Milano, Italy
¹⁰ IRA – INAF, via Gobetti 101, 40129 Bologna, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
¹² INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
¹³ Max Planck Institut fur Astrophysik, 85741 Garching, Germany
¹⁴ Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bvd Arago, 75014 Paris, France
¹⁵ INAF – Osservatorio Astronomico di Brera, via Brera 28, Milan, Italy
¹⁶ Observatoire de Paris, LERMA, 61 Avenue de l'Observatoire, 75014 Paris, France
¹⁷ Centre de Physique Théorique, UMR 6207 CNRS-Université de Provence, 13288 Marseille, France
¹⁸ Universitá di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze 3, 20126 Milano, Italy

Received: 6 April 2006
Accepted: 24 May 2006

Abstract

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 deg². 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 () and a deep () 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 (~ BLAGN per square degree with ) 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) ~ of the AGN brighter than are classified as extended, and this percentage increases to ~42% for those with ; (2) a non-negligible fraction of our BLAGN are lying close to the color-space area occupied by stars in the versus color-color diagram. This leads us to the conclusion that the classical optical-ultraviolet preselection technique, if employed at such deep magnitudes () in conjuction with a preselection of point-like sources, can miss up to ~ 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  Å. 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.