•Textbook (Combes et al.) goes through the old approach of flattened spheroids with a particular mass density as a function of radius. This is perhaps useful review for qualifying exam as an exercise in gravitational physics.
•Key is to use the rotation curve.
•Solutions are appropriately simple for flat curves:
–M(total) = V2rot R/G
(spherical dark matter)
–M(total) = (2/π) V2rot R/G (disk dark matter)
•Where the disk is cut off at r=R, and V = constant (flat
curve) inside r < R.
•Mass increases linearly with r, for V = constant
•Mass/Light ratio increases faster