Galaxy rotation curve from classical Cepheids

Abstract

The Galaxy rotation curve is usually assumed to be flat. However, some galaxies have rotation curves that are lower than the flat rotation curve. In our Galaxy the Keplerian rotation of interstellar clouds in the galactic longitude l=135 was observed. We use a kinematic approach to derive the rotational velocity of classical Cepheids. The rotational velocity was calculated from radial velocity and from proper motion. The derived rotational velocities of Cepheids are between Keplerian rotation and the flat one. We fit a Galaxy rotation model consisting of a black hole, bulge, disk and halo to the rotation curve. The density of dark matter halo is at least 60% less than the value obtained from the flat rotation curve.