ISOCAM survey and dust models of 3CR radio galaxies and quasars

Details ISOCAM survey and dust models of 3CR radio galaxies and quasars ISOCAM survey and dust models of 3CR radio galaxies and quasars

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005esasp.577..325s&link_type=abstract

In: Proceedings of the dusty and molecular universe: a prelude to Herschel and ALMA, 27-29 October 2004, Paris, France. Ed. by A

Statistics

Computation

Agn, Radio Galaxies, Dust, Radiative Transfer, Models

Scientific paper

A survey of all 3CR sources imaged with ISOCAM and ISOPHOT was recently published by Siebenmorgen et al. (2004) and Haas et al. (2004). The sample consists mostly of radio-loud active galactic nuclei (AGN). For each source, we present spatially integrated mid-infrared (MIR) fluxes. In total, we detected 68 objects of the 3CR catalogue, at redshifts z=2.5, and obtained upper limits for 17 objects. The one with the highest redshift is 4C+72.26 at z=3.53. ISOCAM data are combined with other photometric measurements to construct the spectral energy distribution 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 53 cases (~75% 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. 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 1keV. By varying three parameters, luminosity, effective size and extinction, we obtain a fit to the SED for our objects. 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. Our models contain also dust at large (several kpc) distance from the AGN. Such a cold dust component was neglected in previous computations which therefore underestimated the AGN contribution to the far infrared (FIR). However to constrain the cold component we await future Herschel/ALMA photometry. The modelling demonstrates that an AGN heating suffices to explain the ISO broad band data. Starburst activity is not necessary but will be searched for by our IRS Spitzer Space Telescope program and subsequently modeled by a combination of our multi-dimensional radiative transfer models of the AGN torus and the starburst.

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