Issue |
A&A
Volume 451, Number 2, May IV 2006
|
|
---|---|---|
Page(s) | 443 - 456 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20053710 | |
Published online | 02 May 2006 |
Active galactic nuclei in the mid-IR
Evolution and contribution to the cosmic infrared background
1
Max-Planck Institut für extraterrestrische Physik (MPE), Giessenbachstra$\beta$e, Postfach 1312, 85741 Garching, Germany e-mail: matute@mpe.mpg.de
2
Dipartimento di Fisica, Università degli Studi “Roma Tre”, via della Vasca Navale 84, 00146 Roma, Italy e-mail: lafranca@fis.uniroma3.it
3
Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
4
INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
5
INAF, Istituto di Radioastronomia (IRA), via Gobetti 101, 40129 Bologna, Italy
Received:
28
June
2005
Accepted:
30
December
2005
Aims.We study the evolution of the luminosity function (LF) of type-1 and type-2
Active Galactic Nuclei (AGN) in the mid-infrared, derive the
contribution of the AGN to the Cosmic InfraRed Background (CIRB) and the
expected source counts to be observed by at 24 μm.
Methods.We used a sample of type-1 and type-2 AGN selected at 15m
(ISO) and 12
m (IRAS), and classified on the
basis of their optical spectra. Local spectral templates of type-1 and
type-2 AGN have been used to derive the intrinsic 15
m
luminosities. We adopted an evolving smooth two-power law
shape of the LF, whose parameters have been derived using an
un-binned maximum likelihood method.
Results.We find that the LF of type-1 AGN is compatible
with a pure luminosity evolution () model
where
. A small flattening of the faint
(
) slope of the LF with
increasing redshift is favoured by the data. A similar
evolutionary scenario is found for the type-2 population with a
rate kL ranging from ~1.8 to 2.6, depending significantly
on the adopted mid-infrared spectral energy distribution. For type-2
AGN a flattening of the LF with
increasing redshift is suggested by the data, possibly caused by
the loss of a fraction of type-2 AGN hidden within the optically
classified starburst and normal galaxies. The type-1 AGN
contribution to the CIRB at 15
m is
(4.2–12.1)
, while
the type-2 AGN contribution is
(5.5–11.0)
. We
expect that
will observe, down to a flux limit of
mJy, a density of ~1200 deg-2 type-1 and
~1000 deg-2 type-2 optically classified AGN.
Conclusions.AGN evolve in the mid-infrared with a rate
similar to the ones found in the optical and X-rays bands. The derived total
contribution of the AGN to the CIRB (4–10%) and counts should be
considered as lower limits, because of a possible loss of type-2 sources
caused by the optical classification.
© ESO, 2006
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