Is the exponential distribution a good approximation of dusty galactic disks

We investigate how significant the spiral structure is on calculations concerning radiative transfer in dusty spiral galaxies seen edge-on. The widely adopted exponential disk model (i.e. both the stars and the dust are distributed exponen- tially in the radial direction and also perpendicular to the plane of the disk) is now subject to a detailed comparison with a realis- tic model that includes spiral structure for the stars and the dust in the disk. In particular, model images of galaxies with loga- rithmic spiral arms are constructed, such that the azimuthally averaged disk is exponential in radius and in height, as the obser- vations suggest. Then, pure exponential disk models (i.e. with no spiral structure) are used to fit the edge-on appearance of the model images. As a result, the parameters derived after the fit are compared to the real values used to create the spiral-structured images. It turns out that the plain exponential disk model is able to give a very good description of the galactic disk with its parameters varying only by a few percent from their true values.