AAS Meeting #193 - Austin, Texas, January 1999
Session 28. Gas in Galaxies
Oral, Wednesday, January 6, 1999, 2:00-3:30pm, Room 8 (A,B,C)

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[28.03D] An HI aperture synthesis mosaic survey of the Large Magellanic Cloud

Sungeun Kim (MSSSO, UIUC)

This thesis presents the results of an \ion{H}{1} aperture synthesis mosaic of the Large Magellanic Cloud LMC), made by combining data from 1344 separate pointing centres using the Australia Telescope Compact Array (ATCA). The resolution of the mosaiced images is 1.'0 (15 pc, using a distance to the LMC of 50 kpc). This mosaic, with a spatial resolution 15 times higher than that which had been previously obtained, emphasises the turbulent and fractal structure of the ISM on the small scale, resulting from the dynamical feedback of the star formation processes with the ISM. We also have done a widefield panoramic survey of H\alpha emission from the Magellanic Clouds with an imager mounted on the 16-inch telescope at Siding Spring Observatory. This survey produced H\alpha images which are equal to the ATCA survey in area coverage and resolution. This survey allows us to produce a continuum-subtracted image of the entire LMC and surpass the photographic efforts of Davies, et.al. (1976). In contrast with its appearance in the H\alpha image, the LMC is remarkably symmetric in \ion{H}{1} on the largest scales, with the bulk of the \ion{H}{1} residing in a disk of diameter 8.\circ4 (7.3 kpc). Outer spiral structure is clearly seen, though the features appear to be due to differential rotation, and are therefore transient in nature. A good correlation is seen between supershells previously identified in H\alpha (e.g. Meaburn 1980) and \ion{H}{1} structures. The \ion{H}{1} disk appears to be remarkably symmetric, and to have a well organized and orderly, if somewhat complex, rotational field. The mass of the disk component of the LMC is 2.5\times 109 M\odot, and the upper limit to all mass within a radius of 4 kpc is ~.5\times 109 M\odot. The structure of the neutral atomic ISM in the LMC is dominated by \ion{H}{1} filaments combined with numerous shells and holes. We describe the selection and classification criteria for the \ion{H}{1} shell candidates chosen from visual inspection of the \ion{H}{1} data cube of the LMC. We further classify \ion{H}{1} shells or bubbles into 5 different types, based on the comparison of the \ion{H}{1} with their associated H\alpha emission.

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