Gamma-Ray Bursts May Be Biased Tracers of Star Formation

TL;DR

This paper uses galaxy formation simulations to explore how Gamma-Ray Bursts (GRBs) are biased tracers of star formation, showing they favor low-metallicity, less luminous galaxies and may not directly reflect total star formation rates.

Contribution

It demonstrates that GRB formation correlates strongly with low-metallicity, low-luminosity galaxies and suggests that using GRB rates to infer star formation requires careful consideration.

Findings

GRBs preferentially form in low metallicity, less luminous galaxies

The GRB formation rate matches the evolution of low-metallicity star formation from z=0 to z=4

Total star formation rate evolution is weaker than GRB rate evolution by a factor of about 4

Abstract

Based on a simulation of galaxy formation in the standard cosmological model, we suggest that a consistent picture for Gamma-Ray Bursts and star formation may be found that is in broad agreement with observations: GRBs preferentially form in low metallicity environments and in galaxies substantially less luminous that L*. We find that the computed formation rate of stars with metallicity less than 0.1Zsun agrees remarkably well with the rate evolution of Gamma-Ray Bursts observed by Swift from z=0 to z=4, whereas the evolution of total star formation rate is weaker by a factor of about 4. Given this finding, we caution that any inference of star formation rate based on observed GRB rate may require a more involved exercise than a simple proportionality.