The redshift (\(z\)) evolution of the Extragalactic Background Light (EBL) photon density is very important to understand the history of cosmological structure formation of galaxies and stars since the epoch of recombination. The EBL photons with the characteristic spectral energy distribution ranging from ultraviolet/optical to far-infrared provide a major source of opacity of the Universe to the GeV-TeV \(\gamma \)-rays travelling over cosmological distances. The effect of the EBL is very significant through \(\gamma \gamma \rightarrow e^{-} e^{+}\) absorption process on the propagation of the \(\gamma \)-ray photons with energy \(E >\) 50 GeV emitted from the sources at \(z \sim 1\). This effect is characterized by the optical depth (\(\tau \)) which strongly depends on \(E\), \(z\) and density of the EBL photons. The proper density of the EBL photons increases with \(z\) due to expansion of the Universe whereas evolution of radiation sources contributing to the EBL leads to a decrease in the density with increasing \(z\). Therefore, the resultant volumetric evolution of the EBL photon density is approximated by a modified redshift dependence. In this work, we probe evolution of the EBL photon density predicted by two prominent models using cosmic gamma-ray horizon (\(\tau (E,z)=\) 1) determined by the measurements from the Fermi-Large Area Telescope (LAT) observations. The modified redshift dependence of the EBL photon density is optimized for a given EBL model by estimating the same gamma-ray horizon as predicted by the Fermi-LAT observations. We further compare the optical depth estimates in the energy range \(E =\) 4 GeV-1 TeV and redshift range \(z =0.01-1\) from the Fermi-LAT observations with the values derived from the two EBL models to further constrain the evolution of the EBL photon density in the \(z~\sim 1\) Universe.

河外背景光 (EBL) 光子密度的红移 ( \(z\) ) 演化对于了解自重组时代以来星系和恒星的宇宙结构形成历史非常重要。具有从紫外/光学到远红外的特征光谱能量分布的 EBL 光子为在宇宙学距离上传播的 GeV-TeV \(\gamma \)射线提供了宇宙不透明度的主要来源。EBL 通过\(\gamma \gamma \rightarrow e^{-} e^{+}\)吸收过程对\(\gamma \) -射线光子的传播具有非常显着的影响\(E >\)从\(z \sim 1\)处的源发射的 50 GeV. 这种效应的特点是光学深度 ( \(\tau \) ) 强烈依赖于\(E\)、\(z\)和 EBL 光子的密度。由于宇宙的膨胀，EBL 光子的适当密度随着\(z\)增加，而对 EBL 有贡献的辐射源的演化导致密度随着\(z\) 的增加而降低。因此，EBL 光子密度的合成体积演化近似于修正的红移依赖性。在这项工作中，我们使用宇宙伽马射线视界 ( \(\tau (E,z)=\) 1) 来探测由两个著名模型预测的 EBL 光子密度的演变，这些模型由费米的测量值确定- 大面积望远镜 (LAT) 观测。EBL 光子密度的修正红移依赖性通过估计与费米-LAT 观测预测相同的伽马射线层，针对给定的 EBL 模型进行了优化。我们在能量范围进一步比较的光学深度估计\（E = \） 4电子伏特-1 TeV能和红移范围\（Z = 0.01-1 \）从费米与来自两个EBL模型来得出的值-lat观测进一步限制\(z~\sim 1\)宇宙中EBL 光子密度的演化。