SIMBAD references

Active galactic nuclei (AGN) emit substantial energies in the IR range. The observations (Sanders et al. 1989) show substantial variations in the shape of the IR spectrum as well as in the total relative strength of the IR emission. If the IR emission were caused by hot dust one expects to see the silicate feature at 10µm, but observations indicate that the feature is weak. We have solved the radiative transfer problem in detail under the assumption that the IR emission is thermal emission from a silicate dust disc. Optically and geometrically thick disc models are shown to produce both a wealth of spectral shapes and IR strengths in good agreement with Sanders et al. (1989). The silicate feature for these type of discs is very weak over a large range of physical parameters. Weak or absent silicate features are thus not a strong argument against the existence of a dust disc or a normal dust composition.