Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4 from Multiwavelength Galaxy Survey Data

[摘要] Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4fFrom Multiwavelength Galaxy Survey DataWe reconstruct the gamma-ray opacity of the universe out to z approx. <34 using an extensive library of 342 observedgalaxy luminosity function (LF) surveys extending to high redshifts .We cover the whole range from UV to mid-IR(0.1525 micron ) providing for the first time a robust empirical calculation of the gamma gamma optical depth out to several TeV.Here, we use the same database as Helgason et al. where the extragalactic background light was reconstructed fromLFs out to 4.5 micronand was shown to recover observed galaxy counts to high accuracy. We extend our earlier libraryOfLFs to 25micronsuch that it covers the energy range of pair production with gamma -rays (1) in the entire Fermi/LATenergy range, and (2) at higher TeV energies probed by ground-based Cherenkov telescopes. In the absenceof significant contributions to the cosmic diffuse background from unknown populations, such as the putativePopulation III era sources, the universe appears to be largely transparent to gamma-rays at all Fermi/LAT energies outto z approx.. 2 whereas it becomes opaque to TeV photons already at z approx. < 0.2 and reaching tau approx~ 10 at z = 1. Comparingwith the currently available Fermi/LAT gamma-ray burst and blazar data shows that there is room for significantemissions originating in the first stars era.

[发布日期] 2012-10-10

[学科分类] 天体物理学