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We investigate the nature of high-z host galaxies of long gamma-ray bursts (LGRBs) by means of state-of-the-art numerical simulations of cosmic structure formation and evolution of galaxies. We combine results from different runs with various box sizes and resolutions. By assigning to each simulated galaxy the probability to host an LGRB, assumed to be proportional to the mass of young stars, we provide a full description of the physical properties of high-z LGRB host galaxy population. We find that LGRBs at z > 6 are hosted in galaxies with typical star formation rates SFR ≃ 0.03–0.3 M⊙ yr−1, stellar masses M⋆ ≃ 106–108 M⊙ and metallicities Z ≃ 0.01–0.1 Z⊙. Furthermore, the ratio between their doubling time and the corresponding cosmic time seems to be universally equal to ∼0.1–0.3, independently from the redshift. The distribution of their UV luminosity places LGRB hosts in the faint end of the galaxy luminosity function, well below the current capabilities of space- or ground-based optical facilities. This is in line with recent reports of non-detection of LGRB hosts using extremely deep Hubble Space Telescope and Very Large Telescope observations. In conclusion, high-z LGRBs are found to trace the position of those faint galaxies that are thought to be the major actors in the re-ionization of the Universe. [ABSTRACT FROM PUBLISHER]

ABSTRACT Because massive, low-metallicity Population III (PopIII) stars may produce very powerful long gamma-ray bursts (LGRBs), high-redshift GRB observations could probe the properties of the first stars. We analyse the correlation between early PopIII stars and LGRBs by using cosmological N-body/hydrodynamical simulations, which include detailed chemical evolution, cooling, star formation, feedback effects and the transition between PopIII and more standard Population I/II (PopII/I) stars. From the Swift observed rate of LGRBs, we estimate the fraction of black holes that will produce a GRB from PopII/I stars to be in the range 0.028 < fGRB < 0.140, depending on the assumed upper metallicity of the progenitor. Assuming that as of today no GRB event has been associated with a PopIII star, we estimate the upper limit for the fraction of LGRBs produced by PopIII stars to be in the range 0.006 < fGRB < 0.022. When we apply a detection threshold compatible with the BAT instrument, we find that the expected fraction of PopIII GRBs (GRB3) is ∼10 per cent of the full LGRB population at z > 6, becoming as high as 40 per cent at z > 10. Finally, we study the properties of the galaxies hosting our sample of GRB3s. We find that the average metallicity of the galaxies hosting a GRB3 is typically higher than the critical metallicity used to select the PopIII stars, due to the efficiency in polluting the gas above such low values. We also find that the highest probability of finding a GRB3 occurs within galaxies with a stellar mass <107 M⊙, independent of the redshift. [ABSTRACT FROM AUTHOR]

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. As expected, the host sample with no metallicity restriction on the progenitor stars provides a perfect tracer of the cosmic star formation history. When LGRBs are required to be generated by low-metallicity stars, they trace a decreasing fraction of the cosmic star formation rate at lower redshift, as a consequence of the global increase in metallicity. We study the properties of host galaxies up to high redshift (∼9), finding that they typically have low metallicity and that they are small , bluer and younger than the average galaxy population, in agreement with observational data. They are also less clustered than typical L* galaxies in the Universe, and their descendents are massive, red and reside in groups of galaxies with halo mass between and . [ABSTRACT FROM AUTHOR]