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B. K. Moorthy, J. A. Holtzman (New Mexico State University)
We present new results from an ongoing project to measure gradients in the absorption line strengths of spiral bulges. The galaxies in our sample exhibit a wide range of behaviors, from little or no gradient to very steep gradients. A significant fraction show a steeper gradient in the central 2-5 arcsec than farther out. By simultaneously studying indices sensitive to age and metallicity, we find that where gradients are present, they are due primarily to metallicity and not to age. Overall, our results indicate that neither primordial models nor secular evolution can fully account for the observed stellar populations in these bulges. It is likely that some fraction of the stars were formed through collapse or mergers in the early stages of galaxy evolution with subsequent additions or redistibution from recent disk activity. The relative importance of these mechanisms for different types of bulges is discussed.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.