The morphology of the Milky Way - II. Reconstructing CO maps from disc
  galaxies with live stellar distributions
  The arm structure of the Milky Way remains somewhat of an unknown, with
observational studies hindered by our location within the Galactic disc. In the
work presented here we use smoothed particle hydrodynamics (SPH) and radiative
transfer to create synthetic longitude-velocity observations. Our aim is to
reverse-engineer a top down map of the Galaxy by comparing synthetic
longitude-velocity maps to those observed. We set up a system of N-body
particles to represent the disc and bulge, allowing for dynamic creation of
spiral features. Interstellar gas, and the molecular content, is evolved
alongside the stellar system. A 3D-radiative transfer code is then used to
compare the models to observational data. The resulting models display arm
features that are a good reproduction of many of the observed emission
structures of the Milky Way. These arms however are dynamic and transient,
allowing for a wide range of morphologies not possible with standard density
wave theory. The best fitting models are a much better match than previous work
using fixed potentials. They favour a 4-armed model with a pitch angle of
approximately 20 degrees, though with a pattern speed that decreases with
increasing Galactic radius. Inner bars are lacking however, which appear
required to fully reproduce the central molecular zone.
