AN ALTERNATIVE VIEW OF FLAT ROTATION CURVES OF SPIRAL GALAXIES

The present view of flat rotation curves of spiral galaxies relies upon the necessity of a dark mass component to push up the predicted declining portion of the rotation curve, that arises when the galaxy luminous matter and mass to light ratios similar to the ones in the solar neighbourhood are combined. Mass to light ratios obtained from binary galaxy studies are about ten times as large as the values currently assumed for spiral galaxies (Schweizer 1987; Soares 1989). Considering them as the real M/L for spiral galaxies, it implies that the Keplerian rotation curve derived by the combination of these M/L values and the luminous matter distribution of a spiral galaxy lies above observed rotational profiles. Here we argue that a more convincing and coherent approach is to search for the physical processes responsible for pulling down such a predicted rotation curve to the observed levels. Accordingly, a toy model is proposed based on the existence of significant buoyancy forces in the gaseous disk of spiral galaxies. The model has a plausible phenomenological counterpart, and predicts a wide range of rotation curve shapes including flat ones.