Volume 424, Number 2, September III 2004
|Page(s)||531 - 543|
|Published online||23 August 2004|
Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
2 Astronomisches Institut, Ruhr-Universität Bochum (AIRUB), Universitätsstr. 150/NA7, 44780 Bochum, Germany e-mail: email@example.com
3 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
4 European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
5 Space Telescope Science Institute (STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA
Accepted: 1 June 2004
We present the complete set of ISOPHOT observations of 3CR radio galaxies and quasars, which are contained in the ISO Data Archive, providing 75 mid- and far-infrared spectral energy distributions (SEDs) between 5 and 200 μm. For 28 sources they are supplemented with MAMBO 1.2 mm observations and for 15 sources with new submillimetre data from the SCUBA archive. The sample includes flat and steep spectrum quasars, broad and narrow line radio galaxies, as well as Fanaroff-Riley FR 1 and FR 2 types. The SED shapes exhibit a diversity in the infrared (IR), ranging from a smooth dominating synchrotron component in flat spectrum sources to a thermal dust bump around 60-100 μm in steep spectrum sources. The detection rate of a thermal bump in more than 50% of the cases suggests that dust emission may be a general phenomenon in these sources. We check the orientation-dependent unified scheme, in which the powerful FR 2 narrow line galaxies are quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus intercepting the optical-ultraviolet AGN radiation and reemitting it in the infrared. We find that (1) both the quasars and the galaxies show a high mid- to far-infrared luminosity ratio typical for powerful AGNs and (2) – when matched in 178 MHz luminosity – both show the same ratio of isotropic far-infrared to isotropic 178 MHz lobe power. Therefore, from our large sample investigated here we find strong evidence for the orientation-dependent unification of the powerful FR 2 galaxies with the quasars. The distribution of the dust-to-lobe luminosity ratio shows a dispersion which we suggest to be most likely due to the additional influence of evolution and environment superposed on the orientation-dependent unification. We discuss our data also in the frame of the receding torus model. At the high 178 MHz luminosities of our sources above 10 W/Hz we do not find any support for this model in its original formulation and therefore we propose a refinement: The scale height of the torus might not be independent of luminosity, rather it may increase at high luminosities due to the impact of supernovae from starbursts accompanying the AGN phenomena.
Key words: Galaxy: fundamental parameters / galaxies: photometry / galaxies: quasars: general / infrared: galaxies
Based on observations with the Infrared Space Observatory ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.
© ESO, 2004
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