H\,{\sc ii} Regions and Extinction in the Spiral Galaxy M83

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Session 76 -- Spirals I
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[76.01] H\,{\sc ii} Regions and Extinction in the Spiral Galaxy M83

A. L. Hungerford (Western Washington Univ.), S. D. Ryder (Univ.~of Alabama)

We have obtained narrow-band H$\alpha$ imaging and radio continuum synthesis maps for the nearby southern spiral galaxy M83 (NGC~5236) in order to study the variation of the extinction due to dust across the disk of the galaxy. The Australia Telescope Compact Array has been used in 3 of its highest resolution configurations to map M83 in both the 6~cm and the 13~cm continuum, so that non-thermal sources can be distinguished from H\,{\sc ii} regions. By comparing the optical H$\alpha$ and thermal radio continuum flux ratios of individual H\,{\sc ii} regions with those expected from theory, we wish to test whether or not M83 possesses a well-defined radial extinction gradient. Previous searches for such a gradient in M81 (Kaufman et~al.~1987, ApJ, 319, 61) and M51 (van~der~Hulst et~al.~1988, A\&A, 195, 38) have been inconclusive, but the high H\,{\sc ii} region luminosities and significant dust content of M83 make it one of the best candidates for such a study. We present here the preliminary results of an analysis of this data, and outline some implications for the topical issue of opacity in spiral disks.

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