A two-component outer ring and Galactic spiral structure

Abstract

A model of the Galaxy with a ringR1R′2 can explain some large-scale morphological features of Galactic spiral structure. The Carina-Sagittarius arm could consist of two ascending segments of outer ringsR1 andR2, which almost touch each other near the Carina region. The Perseus and Crux arms can be partially identified with the descending segments of ringR2. A model of a two-component outer ring can also explain the existence of some maxima in diagrams of (l,VLSR), which are supposed to correspond to directions tangential to the spiral arms. On the basis of numerical simulations, we propose two sketches of the ring structure of the Galaxy that include a bar, two outer rings, an inner ring and nuclear gas condensation, which may be a nuclear ring. Both sketches can explain the position of the Carina-Sagittarius arm with respect to the Sun. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.