3D self-consistent N-body barred models of the Milky Way II. Gas dynamics

The gas dynamics in the Galactic disc is modeled by releasing an initially axisymmetric SPH component in a completely self-consistent and symmetry-fre e 3D N-body simulation of the Milky Way in which the stellar components dis play a COBE-like bar. The density centre of the stellar bar wanders around the centre of mass and the resulting gas flow is asymmetric and non-station ary, reproducing the HI and CO l - V diagrams only at specific times and th us suggesting a transient nature of the observed inner gas kinematics. The best matching models allow a new and coherent interpretation of the main fe atures standing out of the l - V data within the bar region. In particular, the l - V traces of the prominent offset dustlanes leading the bar major a xis in early-type barred spirals can be unambiguously identified, and the 3 -kpc arm and its non-symmetric galactocentric opposite counterarm are the i nner prolongations of disc spiral arms passing round the bar and joining th e dustlanes at very different galactocentric distances. Bania's clump 1 and 2, and another velocity-elongated feature near l = 5.5 degrees, are interp reted as gas lumps crossing the dustlane shocks. The terminal velocity peak s near l = +/-2.5 degrees are produced by gas along the dustlanes and not b y the trace of the cusped x1 orbit, which passes farther away from the Gala ctic centre. According to these models and to related geometrical constrain ts, the Galactic bar must have an inclination angle of 25 degrees +/- 4 deg rees, a corotation radius of 4.0-4.5 kpc and a face-on axis ratio b/a appro ximate to 0.6.