  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.
