SIMBAD references

The effect of thickness of spiral arms in the dynamics of normal spiral galaxies is examined. We find stable 3D periodic orbits with elliptical projections on the equatorial plane, which can support a spiral pattern with variable thickness. It is shown, that in general these 3D orbits can be found even in models with strong forcing in the z-direction. Differences depending on disk scale lengths and heights as well as on the disk/halo decomposition are outlined. The edge-on shapes of orbits found in the thick spirals are associated with the vertical resonances existing in the potential. The structure of the stable families of periodic orbits suggests that edge-on peanut-shaped profiles are associated to the vertical resonances of the axisymmetric potential and therefore can appear in all types of disk galaxies i.e. not only in systems with a bar perturbation.