Outer Pseudoring in the Galaxy

Abstract

The kinematical features of the Sagittarius (R=5.7 kpc), Carina (R=6.5 kpc), Cygnus (R=6.8 kpc), and Perseus (R=8.2 kpc) arm fragments suggest the existence of two spiral patterns rotating at different angular velocities in the Galaxy. The inner spiral pattern represented by the Sagittarius arm rotates at the angular velocity of the bar, Omega=60(+/-5) km s-1 kpc-1. The outer spiral pattern, which consists of the Carina, Cygnus and Perseus arms, rotates at a smaller angular velocity, Omega=12-22 km s-1 kpc-1. The existence of the outer slow tightly wound spiral pattern and the inner fast spiral pattern can be explained in terms of the results of numerical simulations of the dynamics of the outer pseudoring. The OLR of the bar must be located between the Sagittarius and Carina arms. The Cygnus arm appears as a connecting link between the fast and slow spiral patterns.