The Structure of the Outer Galaxy

outer-galaxy.pngHachisuka et al. report parallaxes and proper motions of three water maser sources in high-mass star-forming regions in the Outer Spiral Arm of the Milky Way. The observations were conducted with the VLBA as part of Bar and Spiral Structure Legacy Survey (BeSSeL) and double the number of such measurements in the literature. The Outer Arm has a pitch angle of 14.9° ± 2.7° and a Galactocentric distance of 14.1 ± 0.6 kiloparsecs toward the Galactic anti-center. The average motion of these sources toward the Galactic Center is 10.7 ± 2.1 km s-1, and there is no sign of a significant fall in the rotation curve out to 15 kiloparsecs from the Galactic Center. The three-dimensional locations of these star-forming regions are consistent with a Galactic warp of several hundred parsecs from the plane.

Image: VLBA parallax and proper motion measurements of maser spot in G097.53+0318 in the outer galaxy. 

Science Team: K. Hachisuka (Yamaguchi University, Shanghai Astronomical Observatory), Y.K. Choi (Korean Astronomy and Space Institute), M.J. Reid (Harvard-Smithsonian Center for Astrophysics), A. Brunthaler (Max-Planck Institut für Radioastronomie), K.M. Menten (Max-Planck Institut für Radioastronomie), A. Sanna (Max-Planck Institut für Radioastronomie), and T.M. Dame (Harvard-Smithsonian Center for Astrophysics).

Publication: Parallaxes of Star-forming Regions in the Outer Spiral Arm of the Milky Way, 2015, Astrophysical Journal, 800, 2.

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