Numerical counterparts of GRB host galaxies

Abstract

We explore galaxy properties in general and properties of host galaxies of gamma-ray bursts (GRBs) in particular, using N-body/Eulerian hydrodynamic simulations and the stellar population synthesis model, starburst99, to infer observable properties. We identify simulated galaxies that have optical star formation rate (SFR) and SFR-to-luminosity ratio similar to those observed in a well-defined sample of 10 host galaxies. Each of the numerical counterparts is found in catalogues at the same redshifts as the observed hosts. The counterparts are found to be low-mass galaxies, with low mass-to-light ratio M/L, recent epoch of formation and high ratio between the SFR and the average of the SFR. When compared to the overall galaxy population, they have colours much bluer than the high-mass star-forming galaxy population. Although their SFRs span a range of values, the specific rates of the numerical counterparts are equal to or higher than the median values estimated at the different redshifts. We also emphasize the strong relationships between the specific SFR and quantities known to reflect the star formation history of galaxies, that is, colour and M/L: at intermediate redshift, the faintest and bluest galaxies are also the objects with the highest specific rates. These results suggest that GRB host galaxies are likely to be drawn from the high specific SFR subpopulation of galaxies, rather than the high SFR galaxy population. Finally, as indicated by our catalogues, in an extended sample, the majority of GRB host galaxies is expected to have specific SFRs higher than found in the magnitude-limited sample studied here.