Galaxies experiencing intense star-formation episodes are expected to be rich in energetic cosmic rays (CRs). These CRs undergo hadronic interactions with the interstellar gases of their host to drive γ-ray emission, which has already been detected from several nearby starbursts. Unresolved γ-ray emission from more distant star-forming galaxies (SFGs) is expected to contribute to the extragalactic γ-ray background (EGB). However, despite the wealth of high-quality all-sky data from the Fermi–LAT γ-ray space telescope collected over more than a decade of operation, the exact contribution of such SFGs to the EGB remains unsettled. We investigate the high-energy γ-ray emission from SFGs up to redshift z = 3 above a GeV, and assess the contribution they can make to the EGB. We show the γ-ray emission spectrum from an SFG population can be determined from just a small number of key parameters, from which we model a range of possible EGB realizations. We demonstrate that populations of SFGs leave anisotropic signatures in the EGB, and that these can be accessed using the spatial power spectrum. Moreover, we show that such signatures will be accessible with ongoing operation of current γ-ray instruments, and detection prospects will be greatly improved by the next generation of γ-ray observatories, in particular the Cherenkov Telescope Array.

中文翻译：

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在河外 γ 射线背景中表征恒星形成星系的特征

经历剧烈恒星形成事件的星系预计将富含高能宇宙射线 (CRs)。这些 CR 与其宿主的星际气体发生强子相互作用，以驱动 γ 射线发射，这已经从附近的几个星暴中检测到。来自更遥远的恒星形成星系 (SFG) 的未解决的 γ 射线发射预计将有助于形成河外 γ 射线背景 (EGB)。然而，尽管费米-LAT γ 射线太空望远镜在十多年的运行中收集了大量高质量的全天数据，但此类 SFG 对 EGB 的确切贡献仍未确定。我们研究了 SFG 的高能 γ 射线发射，直至红移 z = 3 高于 GeV，并评估了它们对 EGB 的贡献。我们展示了来自 SFG 群体的 γ 射线发射光谱可以通过少量关键参数来确定，我们从中模拟了一系列可能的 EGB 实现。我们证明了 SFG 种群在 EGB 中留下了各向异性特征，并且可以使用空间功率谱访问这些特征。此外，我们表明，通过当前 γ 射线仪器的持续运行，可以访问这些特征，并且下一代 γ 射线天文台，特别是切伦科夫望远镜阵列，将大大改善探测前景。