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arXiv 1209.2250astro-ph.CO
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高红移伽玛暴计数作为原初非高斯性的探测

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

Umberto Maio, Ruben Salvaterra, Lauro Moscardini, Benedetta Ciardi

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

我们建议使用高红移长$γ$射线暴（GRB）作为宇宙学工具来限制密度场中的原始非高斯性。通过使用不同的高斯和非高斯模型的不同宇宙学体积的数值，N体，流体动力学，化学模拟，我们自洽地将宇宙恒星形成率密度与相应的GRB率联系起来。假设伽玛暴是宇宙恒星形成的合理示踪剂，我们发现，正的本地非高斯性，描述的非线性参数，\fnl，可能会显着提高伽玛暴率在高红移，$z \gg 6$。如果\fnl为$\sim 1000$，则相对于高斯情况的偏差占几个数量级，\fnl为$\sim 100$占一个数量级，\fnl为$\sim 50$占$\sim 2$因子。这些差异只在大红移时才被发现，而在稍后的时间里，速率趋于收敛。此外，我们的预测和观测到的伽玛射线暴数据之间的比较，在$z > 6$允许排除大的负\fnl，与以前的作品一致。未来在极高的红移（$z\sim 15-20$）下探测到任何长伽玛暴都可能有利于具有正\fnl的非高斯场景。更严格的限制需要更大的高- $z$ GRB完整样品，目前在文献中不可用。通过区分从贫金属人口III制度，和金属富集人口II-I制度的GRB率的贡献，我们得出结论，后者是一个更坚实的示踪剂的基本物质分布，而前者是强烈主导的反馈机制，从第一，大质量，短寿命的恒星，而不是由可能的非高斯波动。这与假设的人口III初始质量函数完全无关。

英文摘要：

We propose to use high-redshift long $γ$-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, $z \gg 6$. Deviations with respect to the Gaussian case account for a few orders of magnitude if \fnl$\sim 1000$, one order of magnitude for \fnl$\sim 100$, and a factor of $\sim 2$ for \fnl$\sim 50$. 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 $z > 6$ allows to exclude large negative \fnl, consistently with previous works. Future detections of any long GRB at extremely high redshift ($z\sim 15-20$) could favor non-Gaussian scenarios with positive \fnl. More stringent constraints require much larger high-$z$ 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.

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