Issue |
A&A
Volume 472, Number 2, September III 2007
|
|
---|---|---|
Page(s) | 443 - 454 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20077611 | |
Published online | 02 July 2007 |
The VVDS type-1 AGN sample: the faint end of the luminosity function
1
Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127, Bologna, Italy e-mail: angela.bongiorno@oabo.inaf.it
2
INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3
Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
4
Integral Science Data Centre, Ch. d'Écogia 16, 1290 Versoix, Switzerland
5
Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
6
Laboratoire d'Astrophysique de Toulouse/Tabres (UMR5572), CNRS, Université Paul Sabatier - Toulouse III, Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
7
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
8
Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
9
IASF-INAF, via Bassini 15, 20133 Milano, Italy
10
Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS - Université de Provence, BP 8, 13376 Marseille Cedex 12, France
11
IRA-INAF, via Gobetti 101, 40129 Bologna, Italy
12
INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
13
Max Planck Institut fur Astrophysik, 85741 Garching, Germany
14
Institut d'Astrophysique de Paris, UMR 7095, 98bis Bd. Arago, 75014 Paris, France
15
School of Physics & Astronomy, University of Nottingham, University Park, Nottingham NG72RD, UK
16
INAF - Osservatorio Astronomico di Brera, via Brera 28, Milan, Italy
17
Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu 96822, Hawaii
18
Observatoire de Paris, LERMA, 61 avenue de l'Observatoire, 75014 Paris, France
19
Centre de Physique Théorique, UMR 6207 CNRS-Université de Provence, 13288 Marseille France
20
Astronomical Observatory of the Jagiellonian University, ul Orla 171, 30-244 Kraków, Poland
21
INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
22
Center for Astrophysics & Space Sciences, University of California, San Diego, La Jolla, CA 92093-0424, USA
23
Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
24
Universitá di Milano-Bicocca, Dipartimento di Fisica - Piazza delle Scienze 3, 20126 Milano, Italy
25
Università di Bologna, Dipartimento di Fisica, via Irnerio 46, 40126 Bologna, Italy
Received:
4
April
2007
Accepted:
26
June
2007
In a previous paper (Gavignaud et al. 2006, A&A, 457, 79), we presented the type-1 Active
Galactic Nuclei (AGN) sample obtained from the first epoch data of the VIMOS-VLT
Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN with
redshift up to and
, selected on the basis of their
spectra. The sample is thus free of the morphological and color selection
biases, that lead to significant incompleteness in the optical surveys of faint
AGN.
In this paper we present the measurement of the Optical Luminosity Function up to
derived from this sample, we compare our results with previous results
from brighter samples both at low and at high redshift and finally, through the
estimate of the bolometric luminosity function, we compare them also with the
results from X-ray and mid-IR selected samples.
Our data, more than one magnitude fainter than previous optical surveys,
allow us to constrain the faint part of the luminosity function up to high
redshift. A comparison of our data with the 2dF sample at low redshift (
) shows that the VVDS data can not be well fitted with the PLE models
derived by previous samples. Qualitatively, this appears to be due to the fact
that our data suggest the presence of an excess of faint objects at low
redshift (
) with respect to these models.
By combining our faint VVDS sample with the large
sample of bright AGN extracted from the SDSS DR3 (Richards et al. 2006b, AJ, 131, 2766) and
testing a number of different evolutionary models, we find that the model which
better represents the combined luminosity functions, over a wide range of
redshift and luminosity, is a luminosity dependent density evolution (LDDE)
model, similar to those derived from the major X-surveys. Such a
parameterization allows the redshift of the AGN space density peak to change
as a function of luminosity and explains the excess of faint AGN that we find
at
. On the basis of this model we find, for the first time from
the analysis of optically selected samples, that the peak of the
AGN space density shifts significantly towards lower redshift going to lower
luminosity objects. The position of this peak moves from
for
to
for
. This result, already found in a number of
X-ray selected samples of AGN, is consistent with a scenario of “AGN cosmic
downsizing”, in which the density of more luminous AGN, possibly associated to
more massive black holes, peaks earlier in the history of the Universe (i.e.
at higher redshift), than that of low luminosity ones, which reaches its
maximum later (i.e. at lower redshift).
Key words: surveys / galaxies: high-redshift / galaxies: quasars: general / galaxies: luminosity function, mass function
© ESO, 2007
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