Three-dimensional distribution of the ISM in the Milky Way galaxy. III. The total neutral gas disk

We present newly obtained three-dimensional gaseous maps of the Milky Way Galaxy: HI, H-2, and total-gas (H1 plus H-2) maps, which were derived from the HI and (CO)-C-12(J=1-0) survey data and rotation curves based on the kinematic distance. The HI and H-2 face-on maps show that the HI disk is extended to a radius of 15-20 kpc and its outskirts are asymmetric to the Galactic center, while most of the H-2 gas is distributed inside the solar circle. The total gas mass within a radius of 30 kpc amounts to 8.0 x 10(9)M(circle dot), 89% and 11% of which are HI and H-2, respectively. The vertical slices show that the outer HI disk is strongly warped and the inner HI and H2 disks are corrugated. The total gas map is advantageous for tracing spiral structures from the inner to outer disk. Spiral structures such as the Norma-Cygnus, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the Orion arms are more clearly traced in the total gas map than ever. All the spiral arms are well explained by logarithmic spiral arms with pitch angles of 11 degrees-15 degrees. The molecular fraction of the total gas is high near the Galactic center and decreases with Galactocentric distance. The molecular fraction is also locally enhanced at the spiral arms compared with the inter-arm regions.