The Vertical Distribution and Kinematics of HI and Mass Models of the Galactic Disk

We present full modelling of tangent point emission of HI as seen in the 21cm transition in the inner Galaxy. We measure the scale height and velocity dispersion of HI as a function of Galactic radius besides the rotation curve and the z-centroid of the atomic layer. The model used takes into account emission from a large path length along the line of sight, corresponding to an interval ( R) of typically 1 in galactic radius; and is parametrized by the scale height of the gas, the centroid in z, the rotation velocity and the velocity dispersion; these parameters are assumed to be constant over the interval R. This model is then t to the 21 cm surveys of Weaver & Williams(1974), Bania & Lockman (1984), and Kerr et al. (1986) to determine the best t parameters. The terminal velocity values are found to be in good agreement with previous measurements. The velocity dispersion is very constant with radius at the theoretically expected value of 9-10 . The Gaussian scale height of the HI layer increases with Galactocentric radius. The centroid of the layer deviates signi cantly from z=0. Apart from small local wiggles, the four quantities measured: terminal velocity VT , velocity dispersion v, scale height z and the centroid z0 show similar variations in the rst and the fourth quadrants. On balancing the turbulent pressure support of the layer against the disk gravitational potential, we con rm that additional support is