Abstract
The rotation curves of 20 spiral galaxies are examined in the light of a toy model (Soares 1992) which has as the main feature the assignment of a high M/L ratio (=30; Ho = 50 km s-1Mpc-1) to the visible matter. The observed rotation of all galaxies can be accommodated without the assumption of a dark halo. Moreover, the suggestion is made that the fact that almost all available rotational velocity measurements are derived from emission lines emitted by gas in galaxies (either neutral or ionized) makes them inappropriate as tracers of the galaxy gravitational potential. To account for that, the model introduces an effective potential mean to describe the hydrodynamics inside a gaseous disk. The general morphology of the curves (i.e., the presence of a plateau in V(r)×r) is interpreted in this framework as a consequence of the hydrodynamical characteristics of disks in galaxies. The Tully-Fisher relation is expressed in terms of model parameters and used as an additional constraint in the process of fitting the model to the observed rotation of the galaxies.
