Talk Title: Constraints on a universal IMF from the entire stellar population
Abstract: We obtain constraints on the slope of a universal stellar initial mass function (IMF) over a range of cosmic star-formation histories (SFH) using z = 0.1 luminosity densities in the range from 0.2 to 2.2 microns. The age-IMF degeneracy of integrated spectra of stellar populations can be broken for the Universe as a whole by using direct measurements of (relative) cosmic SFH from high-redshift observations. These have only marginal dependence on uncertainties in the IMF, whereas, fitting to local luminosity densities depends strongly on both cosmic SFH and the IMF. We fit to these measurements using population synthesis and find the best-fit IMF power-law slope to be -1.15 +- 0.2, assuming a constant slope from 0.5 to 120 solar masses. This is in good agreement with the Salpeter (1955) IMF slope (-1.35). A strong limit of -1.7 is obtained which effectively rules out the Scalo (1986) IMF due to its too low fraction of high-mass stars.
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