标题： 漫射 Ly$α$发射 显示英文标题

标题： Diffuse Ly$α$ Emission

摘要： Ly$\alpha$辐射已成为研究宇宙大尺度结构中弥散气体的强大工具。 在本文中，我们通过后处理来自\texttt{IllustrisTNG}和\texttt{THESAN}项目的宇宙学模拟来研究宇宙中的 Ly$\alpha$辐射。 具体而言，我们在不同红移下计算了来自星系、星系际介质（CGM）和星系间介质（IGM）的 Ly$\alpha$辐射。 我们的结果表明，仅 IGM 就明显低于当前观测的上限。 同时，在$z \lesssim 0.5$处 CGM 超过了观测到的星系贡献，这表明要么内部 CGM 的逃逸分数小于 1，要么当前使用近似自屏蔽处理的光致电离平衡方法不够准确。 星系成分在低红移时也超过了观测值，这表明逃逸分数由于晕质量函数和尘埃增长分布的演化而具有显著的变化，这与观测推导出的逃逸分数一致。 此外，我们的研究结果表明，来自弥散气体（CGM+IGM）的Ly$\alpha$发射在$z \sim 4$时达到峰值，并随着红移降低而减弱。 来自弥散气体的Ly$\alpha$发射主要通过热等离子体的碰撞激发产生。 通过将模型与观测结果进行比较，我们预测的来自弥散气体的Ly$\alpha$发射在$z=1-3$时比观测到的宇宙Ly$\alpha$发射暗$\sim 6$倍。 然而，未来的大型望远镜可能有望探测来自朝向$z>3$的弥漫气体的 Ly$\alpha$发射。 显示英文摘要

摘要： The Ly$\alpha$ emission has emerged as a powerful tool for probing diffuse gas within the large-scale structure of the universe. In this paper, we investigate cosmic Ly$\alpha$ emission by post-processing cosmological simulations from \texttt{IllustrisTNG} and \texttt{THESAN} project. Specifically, we calculate the Ly$\alpha$ emission from galaxies, circum-galactic medium (CGM) and inter-galactic medium (IGM) across various redshifts. Our results show that IGM alone is significantly under the current observational upper limits. Meanwhile, CGM overshoots the observed galaxy contribution at $z \lesssim 0.5$ indicating that either the escape fraction for the inner CGM is less than unity or the current photoionization equilibrium treatment with an approximate self-shielding prescription is less accurate. The galaxy component also overshoots at low redshift, indicating that the escape fraction has strong evolution caused by an evolving halo mass function and dust growth distribution, that agrees with observationally inferred escape fractions. Furthermore, our findings suggest that the Ly$\alpha$ emission from diffuse gas (CGM+IGM) peaked at $z \sim 4$ and diminishes toward lower redshift. The Ly$\alpha$ emission from diffuse gas mainly originates through the collisional excitation of hot plasma. By comparing models with observation, our predicted Ly$\alpha$ emission from diffuse gas remains $\sim 6$ times fainter than the observed cosmic Ly$\alpha$ emission at $z=1-3$. However, future large telescopes may hold great promise to detect Ly$\alpha$ emission from diffuse gas toward $z>3$.