Multi-component models for disk galaxies I. Stellar rotation and anisotropy

We present here a self-consistent, tridimensional model of a disc galaxy co mposed by a number of ellipsoidal distributions of matter having different flattening and density profile. The model is self-consistent and takes into account the observed luminosity distribution, the flattening profile and t he stellar rotation- and velocity dispersion- curves. In this paper we cons idered the particular case of a disc galaxy composed by two spheroidal bodi es: an exponential disc and a bulge following the r(1/4) law. We studied the behavior of the stellar rotation- and velocity dispersion- p rofiles along the sequence of SOs and Spirals, identified by an increasing disc-to-bulge ratio. Inside every class, kinematic curves were produced by changing the relative concentration of the two components and the inclinati on of the galaxy with respect to the line of sight. The comparison with obs ervational data requires only two scaling factors: the total mass of the ga laxy, and the effective radius. The model allows also to detect the presence of anisotropy in the velocity distribution. In the special case of S0s, we explored the sensitivity of th e kinematics of the model by changing the anisotropy and the flattening of the bulge. For intermediate flattening (0.4 less than or equal to b/a less than or equal to 0.85) it is possible to distinguish a change of anisotropy of 15% To show a real case, the model has been applied to the photometric and kine matic data of NGC 5866. We plan to apply these models to a larger database of S0 galaxies in a future paper.