Unified Rotation Curve of the Galaxy - Decomposition into de Vaucouleurs Bulge, Disk, Dark Halo, and the 9-kpc Rotation Dip

We present a unified rotation curve of the Galaxy re-constructed from existing data by re-calculating the distances and velocities for a set of Galactic constants, R-0 = 8 kpc and V-0 = 200 km s(-1). We decomposed it into a bulge with de Vaucouleurs-law profile of half-mass scale radius 0.5 kpc and mass 1.8 x 10(10) M-circle dot, an exponential disk of scale radius 3.5 kpc and 6.5 x 10(10) M-circle dot, and all isothermal dark halo of terminal velocity 200 km s(-1). A r(1/4)-law fit was obtained for the first time for the Milky Way's rotation curve. After fitting by these fundamental structures, two local minima, or dips, of the rotation velocity are prominent at radii 3 and 9 kpc. The 3-kpc clip is consistent with the observed bar. It is alternatively explained by a massive ring with the density maximum at a radius of 4 kpc. The 9-kpc dip is clearly exhibited as the most peculiar feature in the Galactic rotation curve. We explain it by a massive ring of amplitude as large as 0.3 to 0.4-times the disk density with the density peak at a radius Of 11 kpc. This great ring may be related to the Perseus arm, while no peculiar feature of H I-gas is associated.