Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: II. The Molecular Gas Disk

We created a three-dimensional distribution map of molecular gas throughout the Milky Way Galaxy using the latest CO(J =1–0) survey data cube and rotation curve based on the kinematic distance. The radial distribution of the molecular gas shows a central peak and a second peak around 0.5 R0. The thickness of the molecular disk slightly increases from 48 pc to 160 pc with the galactocentric distance within a radius range of 0–11 kpc. We were able to trace the Outer, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the Norma arms as logarithmic spiral arms with pitch angles of 11 − 15. Considering that the pitch angles of the spiral arms are within this range, the Norma and the Outer arms seem to be identified as the same spiral arm. We could also trace a midplane displacement, whose amplitude is nearly constant inside a 10 kpc radius and increases beyond this radius. The ridges of midplane displacement form leading spiral arms.