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arXiv 1208.4364astro-ph.CO
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利用多波长星系巡天数据重建宇宙至z~4的γ射线光子光学厚度

Reconstructing the γ-ray Photon Optical Depth of the Universe to z~4 from Multiwavelength Galaxy Survey Data

Kari Helgason, Alexander Kashlinsky

摘要:

我们利用一个包含342个观测星系光度函数的数据库,重建了z<3-4范围内宇宙的γ射线不透明度。我们覆盖了从紫外到中红外(0.15- 25 mic)的整个范围,首次提供了几TeV的γγ光学深度的可靠经验计算。在这里,我们使用与Helgason等人2012相同的数据库,其中EBL是根据亮度函数重建的,最高可达4.5mic,并且可以将观测到的星系计数恢复到高精度。我们将我们早期的LF库扩展到25 mic,这样它就覆盖了1)整个费米/LAT能量范围内的γ射线对产生的能量范围,以及2)地面切伦科夫望远镜探测的更高TeV能量。在没有来自未知星族的宇宙扩散背景的显著贡献的情况下,例如假定的第三星族时代的来源,宇宙似乎对所有费米/LAT能量的γ射线都是透明的,直到z~2,而对于TeV光子来说,在z<0.2时变得不透明,在z=1时达到τ~10。与现有的Fermi/LAT GRB和blazar数据比较表明,存在起源于第一恒星时代的显著辐射的空间。

英文摘要:

We reconstruct γ-ray opacity of the Universe out to z<3-4 using an extensive library of 342 observed galaxy luminosity function surveys extending to high redshifts. We cover the whole range from UV to mid-IR (0.15-25mic) providing for the first time a robust empirical calculation of the γγ-optical depth out to several TeV. Here, we use the same database as Helgason et al. 2012 where the EBL was reconstructed from luminosity functions out to 4.5mic and was shown to recover observed galaxy counts to high accuracy. We extend our earlier library of LFs to 25mic such that it covers the energy range of pair production with γ-rays 1) in the entire Fermi/LAT energy range, and 2) at higher TeV energies probed by ground-based Cherenkov telescopes. In the absence of significant contributions to the cosmic diffuse background from unknown populations, such as the putative Population III era sources, the Universe appears to be largely transparent to γ-rays at all Fermi/LAT energies out to z~2 whereas becoming opaque to TeV photons already at z<0.2 and reaching τ~10 at z=1. Comparing with the currently available Fermi/LAT GRB and blazar data shows that there is room for significant emissions originating in the first stars era.

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