Nuclear-to-Disk Rotation Curves and Mass-to-Luminosity Ratio in Galaxies

Abstract

High-resolution nuclear-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies show generally a steep nuclear rise and flat rotation from the disk to halo. The high-velocity central rotation indicates massive core within bulges. Since this characteristics is common to most galaxies, the high-velocity central rotation cannot be due to a particular orientation of non-circular motion. Using these rotation curves, we derive the distributions of surface-mass density, and compare directly with observed surface-luminosity distributions. The mass-to-luminosity ratio (M/L) remains constant in the outer bulge and disk, while it increases toward the halo, indicating the massive halo. In the central region, the M/L also increases steeply toward the center, reaching by an order of magnitude greater value than the disk value, which may indicate a massive core of radius about 100 parsecs and mass of the order of E9 Msun. The core may be an object linking a bulge and a massive black hole. (Related data at http://www.ioa.s.u-tokyo.ac.jp/~sofue/)