Scientific Seminars

Host galaxies of Long Gamma-Ray Burst and GRB at high redshift

Maria Angela Campisi
MPI fuer Astrophysik - Garching

2009-06-30    15.00    Merate - POE

We use galaxy catalogues constructed by combining high-resolution N-body simulations with semi- analytic models of galaxy formation to study the properties of Long Gamma-Ray Burst (LGRB) host galaxies. We assume that LGRBs originate from the death of massive young stars and analyse how results are affected by different metallicity constraints on the progenitor stars. We study the properties of host galaxies up to high redshift ( about 9), finding that they typically have low-metallicity (Z<0.5 Z_sun) and that they are small (M<10^9 M_sun), bluer and younger than the average galaxy population, in agreement with observational data. Then, with the same simulation, we study the luminosity function and the rate of GRB. When LGRBs are required to be generated by low-metallicity stars (Z<0.1-0.3 Z_sun), they trace a decreasing fraction of the cosmic star formation rate at lower redshift, as a consequence of the global increase in metallicity, pointing to the conclusion that LGRBs are not good tracers of the star formation rate in the universe. Using the log N-log P diagram for BATSE bursts, we estimate the LF (with and without evolution with redshift) and the formation rate of LGRBs, finding strong constraints for the slope of the power-law. We check the resulting redshift distribution, for SWIFT detector, with an unbiased sample of GRB selected by Jakobsson et al. (2006) uploaded at 2009. We find that models where LGRBs are producted by star with Z<0.3 Z_sun and evolution of the LF are in agreement with the data. We predict to have every 100 LGRB about 2 bright burst with redshift z>6.