Gamma Ray Burst and star formation rates: The physical origin for the redshift evolution of their ratio

TL;DR

This paper models the evolution of gamma-ray burst rates and galaxy star formation, revealing that metallicity evolution and observational biases explain the redshift dependence of their ratio, aligning with current high-redshift observations.

Contribution

It introduces a combined model linking GRB formation efficiency to galaxy metallicity and star formation, explaining the redshift evolution of GRB rates relative to star formation.

Findings

GRB rate per stellar mass is higher in low-metallicity environments.

Metallicity evolution significantly influences GRB rate and its relation to star formation.

Galaxy surveys miss a growing fraction of luminosity density at high redshift.

Abstract

Gamma Ray Bursts (GRBs) and galaxies at high redshift represent complementary probes of the star formation history of the Universe. In fact, both the GRB rate and the galaxy luminosity density are connected to the underlying star formation. Here, we combine a star formation model for the evolution of the galaxy luminosity function from z=0 to z=10 with a metallicity-dependent efficiency for GRB formation to simultaneously predict the comoving GRB rate. Our model sheds light on the physical origin of the empirical relation often assumed between GRB rate and luminosity density-derived star formation rate: Rgrb(z) = \epsilon(z)*SFR_{obs}(z), with \epsilon(z) (1+z)^{1.2}. At z<4, \epsilon(z) is dominated by the effects of metallicity evolution in the GRB efficiency. Our best-fitting model only requires a moderate preference for low-metallicity, that is a GRB rate per unit stellar mass about four times higher for log(Z/Zsun)<-3 compared to log(Z/Zsun)>0. Models with total suppression of GRB formation at log(Z/Zsun)>0 are disfavored. At z>4, most of the star formation happens in low-metallicity hosts with nearly saturated efficiency of GRB production per unit stellar mass. However at the same epoch, galaxy surveys miss an increasing fraction of the predicted luminosity density because of flux limits, driving an accelerated evolution of \epsilon(z) compared to the empirical power-law fit from lower z. Our findings are consistent with the non-detections of GRB hosts in ultradeep imaging at z>5, and point toward current galaxy surveys at z>8 only observing the top 15-20 % of the total luminosity density.