2000ApJ...534..670T

We derive radial profiles of the surface mass density for 19 spiral galaxies directly from their high-resolution rotation curves. Using the corresponding luminosity profiles, we obtain the radial distribution of the mass-to-luminosity ratios (M/Ls) from the inner bulge (around a few hundred parsecs) to the outer disk (≥2-10 kpc) for 11 galaxies (with inclination <70° in order to reduce the influence of the interstellar extinction). The M/Ls in the bulges of two galaxies with sufficient resolution, NGC 4527 and NGC 6946, are found to increase steeply toward the center at radii ∼100-500 pc at rates of 15±3 and 7±2 times per kpc, respectively. Some other galaxies with fairly high resolution also show signs of an increase toward the center. Such an increase may indicate the existence of a new component, a ``massive dark core'', which may be an object linking the bulge and a central black hole. Based on radial variations of the M/Ls, we further discuss the variation of the dark mass fraction in spiral galaxies.