The 2dF Galaxy Redshift Survey: constraints on cosmic star-formation history from the cosmic spectrum

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  • 30 October 2001
Abstract
We present the first results on the history of star formation in the Universe based on the `cosmic spectrum', in particular, the volume-averaged stellar absorption line 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, tracing the history of star formation prior to the epoch of the observed galaxies, 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 models incorporating chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value and that the increase back to z=1 scales as (1+z)^beta with a strong upper limit of beta2 then the SFR for 1<z<5 scales as (1+z)^alpha with alpha1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density which give 1.8<beta<2.9 and -1.0<alpha<0.7.

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