Modelling the SEDs of spiral galaxies

Modelling the UV/optical - infrared/submm SEDs of spiral galaxies observed with Herschel will be an essential tool to quantitatively interpret these observations in terms of the present and past star-formation activity of these systems. In this lecture we describe the SED modelling technique we have developed, its applications and tests of its predictions. We show that both the panchromatic SED modelling of individual galaxies and the B-band attenuation-inclination relation of large statistical samples suggest that spiral galaxies in the nearby Universe behave as optically thick systems in their global properties and large-scale distribution of light (central face-on B-band opacity of approx. 4). However disk galaxies are very inhomogeneous systems, having both optically thick components (e.g. spiral arms), and optically thin components (e.g. the interarm regions), the latter making galaxies transparent to background galaxies.