We present newly obtained three-dimensional gaseous maps of the Milky Way Galaxy ; HI , H _ { 2 } and total-gas ( HI plus H _ { 2 } ) maps , which were derived from the HI and ^ { 12 } CO ( 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 the radius of 15–20 kpc and its outskirt is asymmetric to the Galactic center , while most of the H _ { 2 } gas is distributed inside the solar circle .
The total gas mass within radius 30 kpc amounts to 8.0 \times 10 ^ { 9 } M _ { \odot } , 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 H _ { 2 } disks are corrugated .
The total gas map is advantageous to trace spiral structure 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 with logarithmic spiral arms with pitch angle of 11 \degree – 15 \degree .
The molecular fraction to the total gas is high near the Galactic center and decreases with the Galactocentric distance .
The molecular fraction also locally enhanced at the spiral arms compared with the inter-arm regions .