Dynamics of the Galaxy

Abstract

Our Galaxy is a barred spiral. Recent work based on the COBE NIR data implies a small bulge-bar and a disk with a short scale-length. The corotation radius of the bar is in the range 3-4.5 kpc. The stellar density distribution beyond the end of the bar appears to be perturbed strongly by the Galaxy's spiral arms. Gas flow calculations in corresponding potentials provide a qualitative explanation of many features observed in HI and CO lv-diagrams. These include the 3-kpc-arm and the apparent four-armed spiral structure between corotation and the solar radius. The mass of NIR-luminous matter is constrained by the terminal velocity curve, the Oort limit, and the bulge microlensing observations, and this implies that the Milky Way has a near-maximum disk and a dark halo with a large core radius of ~ 15 kpc. However, we are still some way from a detailed quantitative model for the large-scale dynamics of the Galaxy. I summarize a number of uncertainties as well as how future work might resolve them.