THE UNIVERSAL GALAXY ROTATION CURVE

Analyzing an extended set of selected galaxy rotation curves (with - 17.5 greater-than-or-equal-to M(B) greater-than-or-equal-to - 23.2), we find that for a given luminosity the rotation curves of spiral galaxies within the optical radius are a universal function, V(R) congruent-to 200(L(B)/L(B*))1/4 {1 + [0.12 - 0.24 log (L(B)/L(B*))](R/R(max) - 1)} km s-1 (where L(B*) = 6 x 10(10)h50(-2)L(B). and R(max) = 2.2 disk length scales are two suitable parameterization constants). This result implies strong systematic variations of both the amplitude and the profile of the circular velocity with luminosity, faint (bright) galaxies having low (high) velocities and steep (shallow) velocity gradients. Because luminous disks are self-similar, the observed progression of the shape of rotation curves with luminosity suggests that the dark-to-visible interplay varies with luminosity.