Ivan Baldry

Johns Hopkins University

We present the first results on the history of star formation in the Universe based on the `cosmic spectrum', i.e., the volume-averaged emission spectrum of present day galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that unlike previous studies it is not a luminosity density based estimator. The cosmic spectrum is fitted with models of population synthesis using a method we have developed which decouples continuum and spectral-line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with physical models incorporating consistent chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density.