Gamma-ray bursts and the history of star formation

Popular models for the origin of gamma-ray bursts (GRBs) include short-live d massive stars as the progenitors of the fireballs. Hence the redshift dis tribution of GRBs should track the cosmic star formation rate of massive st ars accurately. A significant proportion of high-mass star formation activi ty appears to occur in regions that are obscured from view in the optical w aveband by interstellar dust. The amount of dust-enshrouded star formation activity taking place has been estimated by observing the thermal radiation from the dust that has been heated by young stars in the far-infrared and submillimetre wavebands. Here we discuss an alternative probe - the redshif t distribution of GRBs. GRBs are detectable at the highest redshifts, and b ecause gamma-rays are not absorbed by dust, the redshift distribution of GR Bs should therefore be unaffected by dust extinction. At present the redshi fts of GRBs can only be determined from the associated optical transient em ission; however, useful information about the prevalence of dust-obscured s tar formation can also be obtained from the ratio of GRBs with and without an associated optical transient. Eight GRBs currently have spectroscopic re dshifts. Once about a hundred redshifts are known, the population of GRBs w ill provide an important test of different models of the star formation his tory of the Universe.