Three‐Dimensional Magnetohydrodynamic Modeling of the Gaseous Structure of the Galaxy: Synthetic Observations

We generate synthetic observations from the four-arm model we presented previously for the Galactic ISM in the presence of a spiral gravitational perturbation. We find that velocity crowding and diffusion have a strong effect in the longitude-velocity ( l - v ) diagram. The velocity-latitude ( v - b ) diagram presents structures at the expected spiral arm velocities, which can be explained by the off-the-plane structure of the arms presented in previous papers of this series. Such structures are observed in the Leiden/Dwingeloo H I survey. The rotation curve, as measured from the inside of the modeled galaxy, shows similarities with the observed one for the Milky Way, although it has large deviations from the smooth circular rotation corresponding to the background potential. The magnetic field inferred from a synthetic synchrotron map shows a largely circular structure but with interesting deviations in the midplane due to distortion of the field from circularity in the interarm regions.