Unseen matter and angular momentum in the Milky Way and other galaxies: Simple two-component models

The present study constructs simple two-component (dark + bright) models for the Milky Way, where both the density distribution and the rotation curve are deduced from known observations. The derived dark-to-bright mass ratio is in the range greater than about 10, in close agreement with the results of more refined approaches, with a weak dependence on the model's geometry. A specific angular momentum is derived for the Milky Way's younger and flatter population and, if angular momentum conservation holds during the evolution, for the whole system. The hypothesis that the whole system is represented by a rigidly rotating polytrope with index n = 0 or n = 1 is used to determine that dark components flatter than 0.7 are an impossibility if protogalaxies gain angular momentum by means of gravitational interactions, while much more flattened dark components might occur for few initial subunits if protogalaxies gain angular momentum by the peculiar velocities of their own subunits.