Lifting the Veil: γ-Ray Bursts as Beacons for Cosmic Star Formation

Abstract

How much of the star formation that has happened over the age of the Universe is obscured? We attempt to address this question by studying the extinction towards γ-ray bursts (GRBs) and their afterglows. Several arguments suggest such an approach. First, GRBs are thought to be associated with the deaths of massive stars and so their formation rate ought to trace that of the massive stars responsible for the observed UV and far-infrared luminosities of both the Lyman break and SCUBA galaxies. Secondly, GRBs are the final phase of the evolution of these massive stars. These stars do not live long enough to travel far from their place of birth, and so GRBs should be located where the stars formed. Thirdly, GRB afterglows are seen in both the optical and X-ray wave-bands, and so we can hope to exploit the differential effects of extinction between the two wave-bands to test whether large amounts of dust and gas are present in the galaxies hosting the GRBs. We can then infer how many of the GRBs occurred in galaxies with both moderate and considerable amounts of dust, likely to be Lyman break and SCUBA galaxies respectively.