The Multi - Phase Medium in the Interstellar Complex N 44

We have obtained high-resolution H i observations of N44, one of the largest H ii complexes in the Large Magellanic Cloud. The distribution and internal motions of the H i gas show dynamic effects of fast stellar winds and supernova blasts. Numerous H i holes are detected, with the most prominent two corresponding to the optically identified superbubbles Shell 1 and Shell 2. The H i gas associated with Shell 1 shows an expansion pattern similar to that of the ionized gas shell, but the mass and kinetic energy of the H i shell are 3–7 times those of the ionized gas shell. The total kinetic energy of the neutral and ionized gas of Shell 1 is still more than a factor of 5 lower than expected in a pressure-driven superbubble. It is possible that the central OB association was formed in a molecular cloud and a visible superbubble was not fully developed until the ambient molecular gas had been dissociated and cleared away. This hypothesis is supported by the existence of a molecular cloud toward N44 and the fact that the apparent dynamic age of the superbubble Shell 1 is much shorter than the age of its OB association LH47. Accelerated H i gas is detected at the supernova remnant 0523−679. The mass and kinetic energy in the associated H i gas are also much higher than those in the ionized gas of 0523−679. Studies of interstellar gas dynamics using ionized gas alone are clearly inadequate; neutral gas components must be included. Subject headings: ISM: bubbles ISM: supernova remnant Magellanic Clouds X-ray, HI, HII: ISM Mount Stromlo and Siding Spring Observatories, ANU, Weston Creek PO, Canberra, ACT 2611, Australia Astronomy Department, University of Illinois at Urbana-Champaign, Urbana, IL 61801 Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping, NSW 2121, Australia Astronomy Department, University of Michigan, Ann Arbor, MI 48109-1090