CO vs HI ROTATIONS OF GALAXIES

Since molecular gas is distributed in the inner disk of galaxies while HI in the outer disk, CO emission can trace the inner rotation curves more accurately than HI. We have derived most-completely sampled rotation curves by combining HI and CO position-velocity diagrams. We show that inner rotation curves have a steep increase within the central few hundred-pc region. The inner behavior of rotation can be fitted by the Miyamoto-Nagai potential, only if a central mass component with scale radius of 100 – 200 pc and a mass of ∼ 3 − 5× 10M⊙• is assumed in addition to the usual bulge. This implies that the central ∼ 100-pc region has a stellar mass density as high as several hundred M⊙•pc −3, orders-of-magnitudes higher than that for a single bulge and disk (several M⊙•pc −3). Such a concentric multi-component structure within a bulge (“bulge in bulge”) may have crucial implication for the dynamical evolution of the central regions of galaxies. Since the molecular gas distribution is closely correlated with optical disk, CO line can be used for the line width-luminosity (Tully Fisher) relation in addition to (instead of) the HI line. We show that the CO-line width-luminosity relation can be a powerful routine method to derive distances of cosmologically-remote galaxies and the Hubble parameter for a significantly large volume of the universe. By applying the CO-line width-luminosity relation to CO-line data by large-aperture mm-wave telescope, we have derived distances to galaxies at cz ∼ 20, 000. In order to measure the inclination and magnitudes, we performed optical imaging observations of thus CO-detected galaxies using the CFHT 3.6-m telescope at high resolution. The radio and optical data have been combined to derive the distances to the galaxies. We further derived the Hubble ratio for these galaxies by applying the CO-line width-luminosity relation. 1