Dynamical models of S0 and Sa galaxies

We present a set of detailed. self-consistent, isotropic dynamical models for disc galaxes. We start from the hypothesis that each galaxy can be decomposed in a bulge, following the r(1/4) law, and a disc with an exponential projected density profile; and that the isodensity surfaces of each component can be represented by similar concentric spheroids. Under these conditions we produce the rotational velocity and velocity dispersion profiles. after taking into account both the asymmetric drift effects and the integration along the line of sight. The model is successfully applied to reproduce the stellar kinematic and photometry of the bulge of the 4 lenticular and early-type spiral galaxies NGC 4565 NGC 7814, NGC 5866 and NGC 4594. For these galaxies detailed stellar kinematical data are available at different positions across the galaxy. The application of our models shows that: 1) For all the galaxies considered in this work. an isotropic model is able to reproduce the whole dynamical data. This is surprising in the special case of NGC 4565, for which previous models were unable to reproduce the velocity distribution without introducing strong anisotropies. 2) We do not need a dark mass halo to reproduce these data. This do not mean that a dark halo is not present, but just that its dynamical effects in these inner regions of the galaxies are negligible. In our opinion. these results strongly support our guess that a complete dynamical model. including both a disc and a bulge component, is needed to understand the structure of the lenticular and Sa galaxies.