A Gas Dynamical Approach to a Face-on View of Our Galaxy

Extract

Recently the bar model for our Galaxy has been an emerging consensus. Here, we investigate how a rotating bar-like bulge affects the global gas dynamics in a disk and compare the longitude-velocity (LV) maps from self-gravitating hydrodynamical simulations, which is based on Wada and Habe (1992), with observed maps of neutral hydrogen and carbon monoxide in the Galaxy. We found that the features on the numerical LV maps depend strongly on four factors: the pattern speed of the bar, the position angle of the Sun, the strength of the bar potential and the ratio of the gas mass to total dynamical mass. We conclude that our Galaxy has a rotating, weak, bar-like bulge (a/b ∼ 0.7) observed from nearly end on (θ_p < 20°). The allowed range of pattern speed of the bar is surprisingly narrow (19±5 km s⁻¹ kpc⁻¹) and is consistent with recent observations of bulge stars. Self-gravity of the interstellar matter is needed to account for the observed molecular ring at a radius of ∼ 4 kpc even if the gas mass fraction to the dynamical mass is small (about 5%).