The Distributions of the Density and the Mass for Spiral Galaxies

Expressions for the distributions of the density and mass of spiral galaxies have been derived for three different orientations of rotation curves with a turn over radius (rt). The central region of the galaxy is found to rotate as a rigid body with a constant density and with a central mass as a function of r3. The density of the outer regions (r > rt) is found to vary inversely with the radius (r), and the corresponding mass is found to be a function of r2. Galaxies with flat rotation curves at (r > rt) has less mass than that with rising up or lowering down rotation curves.