paper

Counts of high-redshift GRBs as probe of primordial non-Gaussianities

arXiv:1209.2250 · doi:10.1111/j.1365-2966.2012.21850.x

Abstract

We propose to use high-redshift long -ray bursts (GRBs) as cosmological tools to constrain the amount of primordial non-Gaussianity in the density field. By using numerical, N-body, hydrodynamic, chemistry simulations of different cosmological volumes with various Gaussian and non-Gaussian models, we self-consistently relate the cosmic star formation rate density to the corresponding GRB rate. Assuming that GRBs are fair tracers of cosmic star formation, we find that positive local non-Gaussianities, described in terms of the non-linear parameter, \fnl, might boost significantly the GRB rate at high redshift, . Deviations with respect to the Gaussian case account for a few orders of magnitude if \fnl, one order of magnitude for \fnl, and a factor of for \fnl. These differences are found only at large redshift, while at later times the rates tend to converge. Furthermore, a comparison between our predictions and the observed GRB data at allows to exclude large negative \fnl, consistently with previous works. Future detections of any long GRB at extremely high redshift () could favor non-Gaussian scenarios with positive \fnl. More stringent constraints require much larger high- GRB complete samples, currently not available in literature. By distinguishing the contributions to the GRB rate from the metal-poor population III regime, and the metal-enriched population II-I regime, we conclude that the latter is a more solid tracer of the underlying matter distribution, while the former is strongly dominated by feedback mechanisms from the first, massive, short-lived stars, rather than by possible non-Gaussian fluctuations. This holds quite independently of the assumed population III initial mass function.

12 pages; MNRAS in press. Chi ha paura muore tutti i giorni

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