Spiral structure of the Milky Way galaxy: observations and theoretical predictions

Abstract: Using observational data on the kinematical properties and density distributions of the subsystems of the Milky Way galaxy, we construct a set of multi-component equilibrium models of its disk. The dynamics of the disk is studied numerically using collisionless-gaseous numerical simulations. After approximately one Gyr, a prominent central bar is formed with a semi-axis of about three kiloparsecs. Outside the central regions, a multi-armed spiral pattern develops, which can be characterized by the superposition of m=2, 3 and 4-armed spiral patterns. The spiral structure and the bar exist for at least 3 Gyr in our simulations. The presence of the bar in the disk of the MilkyWay galaxy imposes rather strict limitations on the density distributions in the subsystems of the MilkyWay galaxy.We find that bar does not form if the radial scale length of the surface density distribution of the disk is more than 2.6 kpc. Analogously, the formation of bar is suppressed in the Milky Way disk in models with a massive and compact stellar bulge. If future GAIA observations confirm the existence of the three-four armed spiral pattern in the disk of the MilkyWay, this will prove the long-term existence of spiral patterns in galactic disks.