The processing of radiation by dust in galaxies

Optical/UV photons and even harder radiation components in galaxies are absorbed and scattered by dust and re-emitted at infrared wavelengths. For a better understanding of the obscured regions of the galaxies detailed models of the interaction of photons with dust grains and the propagation of light are required. A problem which can only be solved by means of numerical solution of the radiative transfer equation. As a prologue we present high angular mid IR observations of galactic nuclei in the spirit of future ELT instrumentation. Dust models are discussed, which are suited to fit the extinction curves and relevant to compute the emission of external galaxies. Self-consistent radiative transfer models have been presented in spherical symmetry for starburst nuclei, in two dimensions for disk galaxies (spirals) and, more recently, in three dimensional configuration of the dust density distribution. For the latter, a highlighting example is the clumpy dust tori around AGN. Modern advances in the field are reviewed which are either based on a more detailed physical picture or progress in computational sciences.