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R. A. Koopmann (Union College & Cornell University)
A quantitative determination of the distribution of H\alpha-emitting gas in normal spiral galaxies is necessary to understand the laws of star formation in spiral disks, the star formation history of the universe, and how galaxy evolution and environment may impact studies of fundamental galaxy properties traced by H-alpha emission. Published studies have presented conflicting results on the coupling of stars and the sites of massive star formation traced by H\alpha. Kennicutt (1989) found for 14 spirals that H\alpha scale lengths, measured from HII region distributions, are comparable to broadband scale lengths. Ryder and Dopita (1994) fit scale lengths to H\alpha surface brightness profiles for a larger sample of 34 spirals, finding H\alpha scale lengths 75% longer on average than in either broadband V or I.
The relative scale lengths of stars and ionized gas are therefore reexamined in a larger sample of 100 Virgo Cluster and field spiral galaxies, via H\alpha and broadband R surface photometry. Results will be searched for trends in relative scale lengths as a function of morphological type, central light concentration, and environment.
The H\alpha scale lengths and extents derived from the imaging data will be compared to the extent of rotation curves derived from long-slit optical spectroscopy for a subset of 78 objects to investigate the effects of spatial inhomogeneity in the ionized gas distribution on rotational velocity widths derived from optical spectroscopy. The H\alpha scale lengths will be used to constrain simulations undertaken by Catinella et al. who are modeling the effects of aperture bias in rotational width measurements derived from the Sloan Digital Sky Survey.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.