U.S.-U.K.-Cooperative Research: Structure of Dwarf IrregularGalaxies

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This award will support ongoing collaborative research between Dr. Paul Hodge, Department of Astronomy, University of Washington and Dr. Harvey MacGillivray, Royal Observatory, Edinburgh, U.K. The researchers propose to study the outer structure of the local group of dwarf irregular galaxies, especially NGC 6822 and IC 1613. Dwarf irregular galaxies are among the most common type of space galaxies, but their structure, especially in their outer regions, remains relatively unexplored. In the local group, the Magellanic Clouds have been the subject of a large number of structural studies; however the next two dwarfs (in order of luminosity) NGC 6822 and IC 1613 are very poorly understood. The outer reaches of these galaxies are likely to provide considerable information about the distant past history of the galaxies themselves, as they are less affected by the recent star-forming events that are found in the denser, central regions. And, even more important, it is the outer, low-density regions that are most affected by external influences, e.g, gravitational interactions with more massive galaxies or gravitational support by a possible massive halo. The investigators propose to use deep, wide-field Schmidt plates to explore the outer structure of these galaxies. The plates will be scanned in Edinburgh with the COSMOS machine and the data will then be processed with the new Edinburgh software, developed to allow work even in very crowded fields. The stars will be cross-identified to allow construction of color-magnitude diagrams from which foreground stars are subtracted. This will enable the investigators to discern the stellar population at different positions and distances from the center of the galaxies. Dr. Hodge is a leading expert in dwarf galaxy structure. The Edinburgh astronomers have many years experience in methods of extracting the most complete and reliable scientific information on galactic structure from star distributions counted automatically from deep Schmidt plates. They have developed analysis techniques specifically designed to overcome the difficulties that can lead to systematic errors in automated star counting due to background change and crowding. The results of this research will be of great importance for our understanding of both stellar and galaxy evolution.