Host galaxies of gamma-ray bursts and their cosmological evolution

We use numerical simulations of large-scale structure formation to explore the cosmological properties of gamma-ray burst (GRB) host galaxies. Among the different subpopulations found in the simulations, we identify the host galaxies as the most efficient star-forming objects, i.e. galaxies with high specific star-formation rates. We find that the host candidates are low-mass, young galaxies with low to moderate star-formation rate. These properties are consistent with those observed in GRB hosts, most of which are subluminous, blue galaxies. Assuming that host candidates are galaxies with high star-formation rates would have given conclusions inconsistent with the observations. The specific star-formation rate, given a galaxy mass, is shown to increase as the redshift increases. The low mass of the putative hosts makes them difficult to detect with present-day telescopes and the probability density function of the specific star-formation rate is predicted to change depending on whether or not these galaxies are observed.