AAS 195th Meeting, January 2000
Session 21. Galaxies Far and Near
Oral, Wednesday, January 12, 2000, 10:00-11:30am, Regency VII

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[21.02] Internal Extinction in Galaxies from A Diameter-Limited Catalog

Juan E. Cabanela (Saint Cloud State University/U of Minnesota)

I have used the Minnesota Automated Plate Scanner (APS) to construct two galaxy catalogs. Comparison of the first of these galaxy catalogs, the Minnesota Automated Plate Scanner Pisces-Perseus Survey (MAPS-PP), to pre-existing galaxy catalogs has led to the discovery that the Uppsala General Catalog and Third Reference Catalog of Galaxies exhibit a very strong measurement bias: their diameters are measured to different isophotes at different galaxy inclinations. Therefore many previous determinations of the diameter function and the internal extinction properties of other galaxies (most of which have relied on one of these two galaxy catalogs) have suffered from a biased diameter measurement.

I avoid this bias by using the APS data (which is obtained using automated computer-based criteria for measuring the structural properties of images digitized from photographic plates) to construct a catalog of over 217,000 galaxies within 30{\arcdeg} of the North Galactic Pole (the MAPS-NGP). The MAPS-NGP is the deepest galaxy catalog constructed over such a large area of the sky and used to re-evaluate previous investigations of the internal extinction in galaxies.

Cross-identification of the MAPS-NGP with other galaxy catalogs allows the determination of effects of internal extinction on galaxies' major-axis isophotal diameters and on their observed flux. I find early-type galaxies show little evidence of internal extinction whereas galaxies later than Sc showing strong internal extinction. The change in internal extinction as a function of morphological type is rather abrupt.

The author(s) of this abstract have provided an email address for comments about the abstract: juan@stcloudstate.edu

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