On the Normalization of the Cosmic Star Formation History

Strong constraints on the cosmic star formation history (SFH) have recentlybeen established using ultraviolet and far-infrared measurements, refining theresults of numerous measurements over the past decade. Taken together, the mostrecent and robust data indicate a compellingly consistent picture of the SFHout to redshift z~6, with especially tight constraints for z<~1. We fit thesedata with simple analytical forms, and derive conservative bands to indicatepossible variations from the best fits. Since the z<~1 SFH data are quiteprecise, we investigate the sequence of assumptions and corrections thattogether affect the SFH normalisation, to test their accuracy, both in thisredshift range and beyond. As lower limits on this normalisation, we considerthe evolution in stellar mass density, metal mass density, and supernova ratedensity, finding it unlikely that the SFH normalisation is much lower thanindicated by our direct fit. Additionally, predictions from the SFH forsupernova type Ia rate densities tentatively suggests delay times of ~3 Gyr. Asa corresponding upper limit on the SFH normalisation, we consider theSuper-Kamiokande (SK) limit on the electron antineutrino flux from pastcore-collapse supernovae, which applies primarily to z<~1. We find consistencywith the SFH only if the neutrino temperatures from SN events are relativelymodest. Constraints on the assumed initial mass function (IMF) also becomeapparent. The traditional Salpeter IMF, assumed for convenience by manyauthors, is known to be a poor representation at low stellar masses (<~ 1 solarmass), and we show that recently favoured IMFs are also constrained. Inparticular, somewhat shallow, or top-heavy, IMFs may be preferred, althoughthey cannot be too top-heavy. (Abridged)Comment: 15 pages, 8 figures, accepted for publication in ApJ, major revisions following referee's comment