The Fermi Gamma-ray Space Telescope has revealed a diffuse γ-ray background at energies from 0.1 gigaelectronvolt to 1 teraelectronvolt, which can be separated into emission from our Galaxy and an isotropic, extragalactic component¹. Previous efforts to understand the latter have been hampered by the lack of physical models capable of predicting the γ-ray emission produced by the many candidate sources, primarily active galactic nuclei^2,3,4,5 and star-forming galaxies^6,7,8,9,10, leaving their contributions poorly constrained. Here we present a calculation of the contribution of star-forming galaxies to the γ-ray background that does not rely on empirical scalings and is instead based on a physical model for the γ-ray emission produced when cosmic rays accelerated in supernova remnants interact with the interstellar medium¹¹. After validating the model against local observations, we apply it to the observed cosmological star-forming galaxy population and recover an excellent match to both the total intensity and the spectral slope of the γ-ray background, demonstrating that star-forming galaxies alone can explain the full diffuse, isotropic γ-ray background.

费米伽马射线太空望远镜揭示了能量从 0.1 吉电子伏特到 1 兆电子伏特的漫射 γ 射线背景，它可以分为来自我们银河系的辐射和各向同性的河外成分¹。^{由于缺乏能够预测许多候选源（主要是活动星系核2,3,4,5}和恒星形成星系^6,7）产生的 γ 射线发射的物理模型，之前理解后者的努力受到阻碍， ^8,9,10，使他们的贡献受到很大限制。在这里，我们提出了一个计算恒星形成星系对 γ 射线背景的贡献的计算，该计算不依赖于经验尺度，而是基于超新星遗迹中加速的宇宙射线相互作用时产生的 γ 射线发射的物理模型星际介质¹¹ . 在根据局部观测验证模型后，我们将其应用于观测到的宇宙学恒星形成星系群，并恢复了与 γ 射线背景的总强度和光谱斜率的极好匹配，证明仅恒星形成星系就可以解释完全漫射、各向同性的 γ 射线背景。