STRUCTURE AND KINEMATICS OF NEUTRAL HYDROGEN GAS IN THE LARGE MAGELLANIC CLOUD

The 21-cm line survey of the LMC of 1982 (Rohlfs et al. 1984) has been extended to cover a field of 8.4-degrees x 8.4-degrees using the same observing and reduction procedures and thus resulting in a homogeneous material consisting of 1 764 line profiles with a resolution of 1.65 km s-1 and sigma(T) almost-equal-to 0.07 K. Decomposing these line profiles into a minimal number (up to at most three) independent Gaussian components we find two separate structural features: a gas disk extending over all of the LMC containing 72% of the HI gas and the L-component at lower radial velocities with 19%. Both features, the disk as well as the L-component, have a reasonably regular distribution of their HI column density and seem to be contiguous structures. The heliocentric radial velocity distribution of the disk has usually been interpreted to be indicative of a warp. If, however, the large angular extent of the LMC is taken into accout, the kinematics can be modeled by that of a flat disk in differential rotation without a large scale warp provided a tangential velocity for the LMC system as postulated by Murai and Fujimoto (1980) is adopted. The rotation curve derived is symmetric with no obvious influence of the bar. For the kinematics of the L-component too a rotating disk gives a reasonable interpretation for the observations. The starburst region 30 Dor seems to be situated in the L-component, it complements the HI distribution to a single, continuous feature. By estimating its ionizing action in a quantitative way it can even be shown that there is a lower limit of 250 - 400 pc for the distance of 30 Dor above the disk of the LMC. Since no line absorption of the disk gas is detected in the source 30 Dor it is assumed to be situated in front of the disk.