http://arxiv.org/abs/1408.2526
Long gamma-ray bursts (LGRBs) have been suggested as close tracers of the underlying star formation rate in the Universe. They could potentially be used to probe the cosmic star formation history (CSFH) with high accuracy due to their high luminosities. We utilise two cosmological simulations from the First Billion Years project to investigate the systematic biases between the CSFH and the LGRB rate at z>5. We populate LGRBs using a Monte-Carlo technique and a sub-selection based on environmental metallicity, progenitor stellar mass and age. Using a physically motivated LGRB progenitor model, we demonstrate that the LGRB rate should trace the CSFH to high redshifts z>5. The measured LGRB rate suggests that LGRBs have opening angles of 0.1 degrees, although the degeneracy with the progenitor model cannot rule out an underlying bias. We demonstrate that proxies that relate the LGRB rate with global LGRB host properties do not reflect the underlying LGRB environment, and are in fact a result of the host galaxy’s spatial properties, such that LGRBs can easily exist in galaxies of solar metallicity. However, we find a sub-class of host galaxies that have low stellar mass and are metal-rich, to the extent that their metallicity dispersions would not allow low-metallicity environments. Detection of a host galaxy with this set of global properties would directly reflect the progenitor’s environment without information on the progenitor’s environment itself. We predict that 10% of LGRBs per year are associated with this subset of host galaxies. The forbidden line emission of these galaxies would be bright enough to be detected by instruments mounted on the James Webb Space Telescope. Such a discovery would place strong constraints on the collapsar model and suggest other avenues to be investigated, e.g., binary progenitor models.
J. Elliott, S. Khochfar, J. Greiner, et. al.
Wed, 13 Aug 14
13/57
Comments: 12 pages, 7 figures, 1 table, submitted to MNRAS, comments welcome
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