The Multiphase Medium in the Interstellar Complex N44

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Abstract
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 LH 47. Accelerated H I gas is detected at SNR 0523-679. The mass and kinetic energy in the associated H I gas are also much higher than those in the ionized gas of SNR 0523-679. Studies of interstellar gas dynamics using ionized gas alone are clearly inadequate; neutral gas components must be included.
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