The Face-on View of the Milky Way: Gas Dynamics in the COBE NIR Bulge   and Disk
  We report simulations of the gas flow in the gravitational potential of the COBE NIR bulge and disk. These models lead to four--armed spiral structure between corotation of the bar and the Sun, in agreement with the observed spiral arm tangents. The 3-kpc-arm is identified with one of the arms emanating from the ends of the bar. 
Peter Englmaier and Ortwin E. Gerhard