Numerical counterparts of GRB host galaxies

Properties of host galaxies of gamma-ray bursts (GRBs) are investigated, using NT-body/Eulerian hydrodynamic simulations and the stellar population synthesis model, Starburst, 99, to infer observable properties. The simulations include gravitation, hydro-dynamical shocks, and radiative cooling, as well as a phenomenological description of galaxy formation. We first focus on the overall population at intermediate redshifts and emphasize the strong relationships between the specific star formation rate (SFR) and the epoch of formation, color index and mass-to-light ratio, quantities known to reflect the star formation history of galaxies. The faintest and bluest galaxies are objects with the highest specific rates. Faint and blue colors are common properties among the population of GRB host galaxies. We then consider a well-defined sample of observed GRB host galaxies with optical estimates of SFR and SFR-to-luminosity ratios and look for their numerical counterparts by selecting objects that have both values nearest to those of the observed host galaxies. Comparing the numerical counterparts to the overall simulated galaxy population at different redshifts suggests that GRB host galaxies are a particular sub-population of galaxies, likely to be drawn from the high specific SFR population, rather than the high SFR galaxy population. In a separate, preliminary study, we address the link between the cosmological evolution of galaxy properties and the properties of the gas surrounding galaxies by tracing the history of galaxies through their main progenitors. We show that high specific SFRs tend to occur in the early evolutionary stages of galaxies. GRB host galaxies may thus be a powerful way to select those proto-galaxies and contribute to our understanding of galaxy evolution.