Rotation Curve and Mass Distribution in the Galactic Center --- From Black Hole to Entire Galaxy ---

TL;DR

This study constructs a comprehensive rotation curve of the Milky Way from the central black hole to the outer halo, revealing detailed mass distribution and the structure of the galactic bulge.

Contribution

It provides the first continuous rotation curve covering from 1 parsec to hundreds of kiloparsecs, linking the galaxy's kinematics from the black hole to dark matter halo.

Findings

Galactic bulge consists of two exponential components.

De Vaucouleurs law does not fit the bulge mass profile.

Rotation curve spans from 1 pc to several hundred kpc.

Abstract

Analyzing high-resolution longitude-velocity (LV) diagrams of the Galactic Center observed with the Nobeyama 45-m telescope in the CO and CS line emissions, we obtain a central rotation curve of the Milky Way. We combine it with the data for the outer disk, and construct a logarithmic rotation curve of the entire Galaxy. The new rotation curve covers a wide range of radius from r ~ 1 pc to several hundred kpc without a gap of data points. It links, for the first time, the kinematical characteristics of the Galaxy from the central black hole to the bulge, disk and dark halo. Using this grand rotation curve, we calculate the radial distribution of surface mass density in the entire Galaxy, where the radius and derived mass densities vary over a dynamical range with several orders of magnitudes. We show that the galactic bulge is deconvolved into two components: the inner (core) and main bulges. Both the two bulge components are represented by exponential density profiles, but the de Vaucouleurs law was found to fail in representing the mass profile of the galactic bulge.