2011MNRAS.418.2508M

A model of the Galaxy with a ring R₁R'₂ can explain some large-scale morphological features of Galactic spiral structure. The Carina–Sagittarius arm could consist of two ascending segments of outer rings R₁ and R₂, which almost touch each other near the Carina region. The Perseus and Crux arms can be partially identified with the descending segments of ring R₂. A model of a two-component outer ring can also explain the existence of some maxima in diagrams of (l, V_LSR), 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.