Three-dimensional distribution of the ISM in the Milky Way Galaxy: I. The H I disk

We derived the three-dimensional distribution of H I gas in the Milky Way Galaxy using the latest H I survey data cubes and rotation curves. The distance of the H I gas was determined by the kinematic distance using a rotation curve. We solved the near-far problem in the inner Galaxy by a fitting method which involves introducing a model of vertical H i distribution. In our resultant maps we could trace three prominent arms: the Sagittarius-Carina arm, the Perseus arm, and the Outer arm. These three arms were found to be logarithmic spiral arms. The pitch angles of the Sagittarius-Carina, Perseus, and Outer arms were estimated to be about 11degrees, 18degrees, and 7degrees, respectively. The Sun is located in a region rich in H I gas between the Sagittarius-Carina arm and the Perseus arm. The H I disk shows large and asymmetric warping in the outer disk: the H i disk goes up to about 1.5 kpc above the Galactic plane in the northern hemisphere, and down to about I kpc in the southern hemisphere, which means asymmetric warping. The inner H i disk is also found to be tilting. The radius of the H I disk is about 17 kpc and the H I mass within this radius is estimated to be 2.5 x 10(9) Mcircle dot, which corresponds to 1.5% of the dynamical mass predicted from the rotation curve. We also found that the H I outskirt is largely swelling in the fourth quadrant, and hence the Galaxy is significantly lopsided. The scale-height of the H I layer increases with the radius, and is correlated with the H i volume density at the centroid of the H I layer.