Rotation curve of the Milky Way

Abstract

We use SEGUE and Hipparcos data to restrict the behaviour of the rotation curve of the Milky Way in the solar neighbourhood. Then we construct a density model of the Milky Way which best reproduces the available observations of the rotation curve and is consistent with the density constraints in the solar neighbourhood. This equation assumes constancy of the shape of the velocity ellipsoid, its alignment with the axes of spherical coordinate system, and an exponential disc with scalelength Rd and a constant thickness. Thus we find the circular velocity vc for our samples. We assume the local circular velocity vc� = 231km/s, the local standard of rest from (3), and the disc scalelength Rd = 2.5kpc. The resulting rotation curve is presented in the left panel of Fig. 1. SEGUE sample is plotted with purple line, GCS is separated in 5 colour bins, which are plotted with points of different colours. Mean rotational velocities without correction for asymmetric drift being implemented are plotted with dashed lines, the corrected circular velocity with solid lines. The consistency of the circular velocity for GCS colour bins with different mean velocities demonstrates viability of the adopted value of Rd and other our assumptions. The rotation curve for the SEGUE data appears to be essentially flat in the solar neighbourhood. At least, it obviously demonstrates no drastic dip between 8 and 10kpc, as it was assumed in (6).