SED models of AGN
  Present AGN models aiming to account for the observed infrared SEDs consider a physical description of the dust and a solution of the radiative transfer problem. Mid infrared spectra obtained at different spatial scales are presented. They show that PAH bands are detected in starburst regions but significantly reduced near the centre of AGN. This may be explained by examining the heating mechanism of PAHs after hard photon interactions. On the radiative transfer side first a most economic model is presented where three parameters, luminosity, effective size and extinction of the nucleus are varied to obtain SED fits. A full grid of model spectra are made available at: "http://www.eso.org/~rsiebenm/agn_models". This model is sufficient to account for ISO broad band data of a sample of 68 radio galaxies and quasars of the 3CR catalogue. The hot dust component detected is mainly due to small grains and PAHs. In such models, type 1 AGNs are represented by a compact dust distribution with warm grains and weak PAH emission. In AGNs of type 2, the dust appears to be more extended, relatively colder and PAH bands are strong. Realistic AGN models which are consistent with the unification need to explain the overall absence of the 9.7mic. silicate emission feature. This can be done by considering various geometries (tapered discs). Models which combine AGN and starburst activity are presented for galaxies with hidden broad line region. It is found that the AGN torus dominate the mid IR continuum emission and that the starbursts dominate the PAH band as well as the far infrared and submillimeter emission. 
Ralf Siebenmorgen and Andreas Efstathiou