标题： 来自弥散气体的宇宙莱曼$α$发射 显示英文标题

标题： Cosmic Ly$α$ Emission from Diffuse Gas

摘要： Ly$\alpha$发射已成为探测宇宙大尺度结构中弥散气体的有力工具。 本文通过对 \texttt{IllustrisTNG} 和 \texttt{THESAN} 项目的宇宙学模拟进行后处理，研究了宇宙的 Ly$\alpha$发射。 具体来说，我们计算了不同红移的星系、星系间介质 (IGM) 和星系际介质 (CGM) 的 Ly$\alpha$发射。 结果表明，仅 IGM 的 Ly$\alpha$ 发射明显低于目前的观测上限。 同时，CGM 在 $z \lesssim 0.5$ 处超过了观测到的星系贡献，这表明要么是内层 CGM 的逃逸分数小于 1，要么是当前采用近似自屏蔽方案的光电离平衡处理方法不够准确。 星系成分在低红移时也会超过正常值，表明逃逸分数具有强烈的演化，这是由不断演变的晕质量函数和尘埃增长分布引起的，这与观测推断的逃逸分数一致。 此外，我们的研究结果表明，来自弥散气体（CGM+IGM）的Ly$\alpha$辐射在红移为$z \sim 4$时达到峰值，并随着红移降低而减弱。 弥散气体中的Ly$\alpha$辐射主要来源于高温等离子体的碰撞激发。 通过将模型与观测结果进行比较，我们预测的弥散气体产生的Ly$\alpha$辐射在红移$z=1-3$处比观测到的宇宙Ly$\alpha$辐射弱$\sim 6$倍。 然而，未来的大型望远镜可能很有希望探测到来自弥散气体的Ly$\alpha$发射线向$z>3$。 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 $z>3$.