The Local Metallicity -- Surface Brightness Relationship in Galactic Disks

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Session 89 -- Clusters of Galaxies - Galaxy Evolution
Oral presentation, Wednesday, 11, 1995, 10:00am - 11:30am

[89.04] The Local Metallicity -- Surface Brightness Relationship in Galactic Disks

S. D. Ryder (University of Alabama)

Multi-aperture spectrophotometry of H\,{\sc ii}~regions in 6 southern spiral galaxies has been used to confirm the existence of a universal correlation between the gas-phase oxygen abundance and the mean underlying $I$~band surface brightness at the radial distance of the H\,{\sc ii}~region. Such a relationship allows us to circumvent the normal scale dependencies of abundance gradients, and to attempt to model the evolution of a generic galaxy, instead of just our own Milky Way. Although the simple ``closed-box'' model of galaxy evolution predicts almost the right form of this relationship, a more realistic multi-zone model employing exponentially decreasing gas infall provides an extremely good fit to the observational data, provided the expected enriched gas return from dying intermediate- and low-mass stars shedding their envelopes at late epochs is properly taken into account . This same model, with a star formation law based upon self-regulating star formation in a three-dimensional disk (Dopita \& Ryder 1994, ApJ, 430, 163), is equally capable of accounting for the analogous relationship between recent massive star formation and stellar surface brightness (Ryder \& Dopita 1994, ApJ, 430, 142).

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