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E. H. Wehner, J. S. Gallagher (U of Wisconsin - Madison), W. R. Brown (Harvard Smithsonian CfA)
There are two major theories of galaxy evolution, monolithic collapse and the hierarchical merging scenario. The former model describes spheroidal galaxy formation as occurring in one large initial burst of star formation, followed by passive galaxy evolution, as the stars slowly age. In contrast, the hierarchical merging scenario describes galaxy formation as a slower, ongoing process, where large galaxies are created by numerous mergers of smaller objects. This model tends to produce more star formation at later times. The star formation rate density as a function of redshift can distinguish between these two models by showing us when most of the stars in the universe were made. Over the past ten years, various measures of this star formation history have been made. All studies indicate a steep increase in the star formation rate from z = 0 to z = 1, although the magnitude of this jump remains in question. Studies using UV data suggest a factor of ~10 increase between now and z = 1, whereas studies including submillimeter sources (dust enshrouded star formation) indicate a factor of ~ 30 increase. It is possible that the UV is simply missing most of the universe's star formation, but it is also possible that submillimeter sources are rare objects, and including them creates a biased sample. Our study uses V and R photometry (Brown et al. 2001, AJ, 122, 714) of 1,255 Century Survey galaxies to place constraints on this variation in star formation rate from the present time to z ~1. We create a simple model assigning V-R colors to various weightings of stars formed in an initial burst versus those formed at a constant rate over time. Our results are consistent with a factor of 10 increase between now and z ~1-2.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.