Issue |
A&A
Volume 421, Number 1, July I 2004
|
|
---|---|---|
Page(s) | 129 - 145 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20035908 | |
Published online | 11 June 2004 |
ISOCAM survey and dust models of 3CR radio galaxies and quasars *,**
1
European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching b. München, Germany
2
Space Telescope – European Coordinating Facility, Karl-Schwarzschildstr. 2, 85748 Garching b. München, Germany
3
Max-Planck-Institut for Radioastronomy, Auf dem Hügel 69, Postfach 2024, 53010 Bonn, Germany
4
Astronomisches Institut, Ruhr-Universität, Universitätsstr. 150, 44780 Bochum, Germany
Corresponding author: R. Siebenmorgen, rsiebenm@eso.org
Received:
19
December
2003
Accepted:
18
March
2004
We present a survey of all 3CR sources imaged with ISOCAM
onboard the Infrared Space Observatory (ISO). The sample
consists mostly of radio-loud active galactic nuclei (AGN). For each
source, we present spatially integrated mid-infrared (MIR,
m) fluxes measured from newly calibrated ISOCAM images. In
total, we detected 68 objects of the 3CR catalogue, at redshifts
, and obtained upper limits for 17 objects. In addition, we
detected 10 galaxies not listed in the 3CR catalogue. The one with
the highest redshift is 4C+72.26 at
. ISOCAM data are
combined with other photometric measurements to construct the spectral
energy distribution (SED) from optical to radio wavelengths. The MIR
emission may include synchrotron radiation of the AGN, stars of the
host galaxy or dust. Extrapolation of radio core fluxes to the MIR
show that the synchrotron contribution is in most cases negligible.
In order to describe dust emission we apply new radiative transfer
models. In the models the dust is heated by a central source which
emits photons up to energies of 1 keV. By varying three parameters,
luminosity, effective size and extinction, we obtain a fit to the SED
for our objects. Our models contain also dust at large (several kpc)
distances from the AGN. Such a cold dust component was neglected in
previous computations which therefore underestimated the AGN
contribution to the far infrared (FIR). In 53 cases (~
% of
our detected 3CR sources), the MIR emission can be attributed to dust.
The hot dust component is mainly due to small grains and PAHs.
The modelling demonstrates that AGN heating suffices to explain the
ISO broad band data, starburst activity is not necessary. In the
models, a type 1 AGN is represented by a compact dust distribution,
the dust is therefore very warm and emission of PAHs is weak because
of photo-destruction. In AGNs of type 2, the dust is relatively
colder but PAH bands are strong.
Key words: infrared: galaxies / galaxies: ISM / ISM: dust, extinction
© ESO, 2004
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