Ly$\alpha$ forest absorption spectra decomposed into multiple Voigt profile components (clouds) allow us to study clustering of intergalactic medium (IGM) as a function of HI column density ($N_{\rm HI}$). Here, we explore the transverse three-point correlation ($\zeta$) of these Ly$\alpha$ clouds using mock triplet spectra obtained from hydrodynamical simulations at $z \sim 2$ on scales of 1-5 $h^{-1}$cMpc. We find $\zeta$ to depend strongly on $N_{\rm HI}$ and scale and weakly on angle ($\theta$) of the triplet configuration. We show that the "hierarchical ansatz" is applicable for scales $\ge~ 3h^{-1}$cMpc, and obtain a median reduced three-point correlation (Q) in the range 0.2-0.7. We show, $\zeta$ is influenced strongly by the thermal and ionization state of the gas. As found in the case of galaxies, the influence of physical parameters on Q is weaker compared to that of $\zeta$. We show difference in $\zeta$ and Q between different simulations are minimized if we use appropriate $N_{\rm HI}$ cut-offs corresponding to a given baryon over-density ($\Delta$) using the measured $N_{\rm HI}~vs~\Delta$ relationship obtained from individual simulations. Additionally, we see the effect of pressure broadening on $\zeta$ in a model with artificially boosted heating rates. However, for models with realistic thermal and ionization histories the effect of pressure broadening on $\zeta$ is weak and sub-dominant compared to other local effects. We find strong redshift evolution shown by $\zeta$, mainly originating from the redshift evolution of thermal and ionization state of the IGM. We discuss the observational requirements for the detection of three-point correlation, specifically, in small intervals of configuration parameters and redshift.

中文翻译：

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IGM 在 z ∼ 2 的三点和两点空间相关性：使用模拟的基于云的分析

Ly$\alpha$ 森林吸收光谱分解为多个 Voigt 剖面分量（云），使我们能够研究作为 HI 柱密度（$N_{\rm HI}$）函数的星系际介质（IGM）的聚类。在这里，我们使用从水动力模拟中获得的模拟三重谱探索这些 Ly$\alpha$ 云的横向三点相关性（$\zeta$）在 $z\sim 2$ 的尺度为 1-5 $h^{- 1}$cMpc。我们发现 $\zeta$ 强烈依赖于 $N_{\rm HI}$ 和比例，而弱依赖于三元组配置的角度 ($\theta$)。我们表明“分层 ansatz”适用于尺度 $\ge~ 3h^{-1}$cMpc，并在 0.2-0.7 范围内获得中值减少的三点相关 (Q)。我们表明，$\zeta$ 受气体的热态和电离态的影响很大。正如在星系中发现的那样，与$\zeta$相比，物理参数对Q的影响较弱。如果我们使用适当的 $N_{\rm HI}$ 截断值对应给定的重子超密度 ($\Delta$)，使用测量的 $N_{ \rm HI}~vs~\Delta$ 关系从单个模拟中获得。此外，我们在人为提高加热速率的模型中看到了压力加宽对 $\zeta$ 的影响。然而，对于具有真实热和电离历史的模型，与其他局部效应相比，压力展宽对 $\zeta$ 的影响是微弱和次要的。我们发现 $\zeta$ 显示出强烈的红移演化，主要源于 IGM 的热态和电离态的红移演化。