Cosmic Star Formation, Gamma-Ray Burst Rate at high redshift and Cosmic Chemical Evolution

Abstract

Recent optical/IR/UV observations and Gamma-ray burst rate determinations have led to significant progress in constraining the star formation rate (SFR) at high redshift. The SFR is a fundamental quantity since it is used to predict, among others, the ionization history of the Universe, the evolution of the cosmic chemical abundances and the supernova rates as a function of the redshift. Such predictions are made here using a hierarchical model for structure formation. In this context, we focus our attention on the origin and evolution of a typical r process element, Europium, in two possible scenarios for the main astrophysical production site, namely core collapse supernovae (CCSN) and neutron star mergers (NSM). We find that this model favours NSM as the main r process site, specifically at low metallicity, and in addition, constrains the NSM time delay to ∼ 0.1-0.2 Gyr. On the other hand, the evolution of Eu abundances puts also a constraint on the merger rate, which allows an independent prediction of the expected merger rate in the horizon of the gravitational wave detectors advanced Virgo/ad LIGO, as well as a prediction for the expected rate of electromagnetic counterparts to mergers in large NIR surveys. Finally, while this model favors NSM as the main r-process site, more observations at very low metallicity and improved predictions from the nucleosynthetic evolution of massive stars are needed to confirm this result.