Towards an Understanding of the Dynamics of the Milky Way

Abstract

We report on the proper motions of Galactic water masers relative to an adjacent extragalactic continuum source measured by VLBA multi-epoch phase referencing observations for two interstellar regions. We estimated the distance to these Galactic maser sources by their proper motions. The distance to W3(OH) are 2.05 +/- 0.23 and 2.26 +/- 0.09 kpc by annual parallax of each maser feature, and IRAS 21008 + 4700 is 5.26 kpc by the rms deviation from the least squares method fitting for its proper motion. These results provide us a first step of an understanding of the dynamics of the Milky Way.