INTERARM FEATURES IN GASEOUS MODELS OF SPIRAL GALAXIES

We study the response of gaseous disks, under the influence of spiral perturbations. In particular we compare the morphology of spiral arms and interarm regions in SPH models, with Population I features observe d on B images of normal, grand design spiral galaxies. We place the 4/ 1 resonance at the end of the strong symmetric spiral arms of these ga laxies. This basic hypothesis, leads to the appearance of features in the mod els similar to those observed, while other assumptions for the spiral pattern speed did not show the same good agreement. The ''4/1' ' models, especially when a weak m=1 component is included in the impo sed spiral potential, reproduce many morphological aspects of these ga laxies. The main result is that the 4/1 resonance generates a clear si gnature in galaxies, namely a bifurcation of the arms typical for the morphology of normal, late-type, grand design spirals. This bifurcatio n also gives rise to the main interarm features.