Reconciling the GRB rate and star formation histories

TL;DR

This paper investigates why gamma-ray bursts (GRBs) do not follow the overall star formation rate, finding they originate mainly in low-mass, low-metallicity dwarf galaxies, which explains their concentration in high star formation regions.

Contribution

It identifies the specific galaxy properties that reproduce the observed GRB rate, linking GRB hosts to dwarf, low-metallicity galaxies and explaining their spatial distribution.

Findings

GRBs predominantly occur in galaxies with stellar mass below 10^10 Msun

GRB host galaxies are anti-biased and located in filaments and voids

GRB hosts are dwarf galaxies with low metallicity

Abstract

While there are numerous indications that GRBs arise from the death of massive stars, the GRB rate does not follow the global cosmic star formation rate and, within their hosts, GRBs are more concentrated in regions of very high star formation. We explain both puzzles here. Using the publicly available VESPA database of SDSS Data Release 7 spectra, we explore a multi-parameter space in galaxy properties, like stellar mass, metallicity, dust etc. to find the sub-set of galaxies that reproduce the recently obtained GRB rate by Wanderman & Piran (2010). We find that only galaxies with present stellar masses below < 10^{10} Msun and low metallicity reproduce the observed GRB rate. This is consistent with direct observations of GRB hosts and provides an independent confirmation of the nature of GRB hosts. Because of the significantly larger sample of SDSS galaxies, we compute their correlation function and show that they are anti-biased with respect to the dark matter: they are in filaments and voids. Using recent observations of massive stars in local dwarfs we show how the fact that GRB hosts galaxies are dwarfs can explain the observation that GRBs are more concentrated in regions of high star formation than SNe. Finally we explain these results using new theoretical advances in the field of star formation.