恒星形成盘星系中的紫外辐射场：使用 TIGRESS-NCR 的数值模拟
Ultraviolet Radiation Fields in Star-Forming Disk Galaxies: Numerical Simulations with TIGRESS-NCR
AI总结：
本研究利用 TIGRESS-NCR 高分辨率模拟刻画盘星系 FUV/LyC 辐射场，评估近似辐射模型，并提出由中红外和 EM 观测反演气体密度、中性比例及电离光子平均自由程的方法。
摘要：
通过采用自适应光线追踪（ART）进行辐射转移，同时演化气体磁流体力学、热力学和光化学的数值模拟，可以在多相星际介质的真实模型中获得紫外（UV）辐射场及其效应的高分辨率视图。在此，我们分析 TIGRESS-NCR 模拟结果，这些模拟同时追踪远紫外（FUV）波段和莱曼连续谱（LyC）；前者对光电加热和 PAH 激发很重要，后者使氢光电离。我们考虑代表太阳邻域和银河系内部条件的两个模型，刻画 UV 辐射场的空间分布与时间变化，并量化它们与气体的相关性。我们将四种 FUV 近似模型与模拟值进行比较，以评估在无法使用完整 ART 时的替代方案。通过将 FUV 辐射与密度卷积，我们生成尘埃发射的模拟图。我们提出一种校准中红外观测（例如来自 JWST 的观测）的方法，以获得高分辨率气体面密度图。随后我们考察 LyC 辐射场，发现暴露于该辐射的大多数气体处于电离—复合平衡状态，并具有较低的中性比例。此外，我们将电离参数表征为环境的函数。利用 LyC 辐射场的简化模型，我们生成发射量度（EM）的合成图。我们表明，该简化模型可用于从星系中观测到的 EM 图提取光电离气体中性比例和电离辐射平均自由程的估计值。
英文摘要：
With numerical simulations that employ adaptive ray-tracing (ART) for radiative transfer at the same time as evolving gas magnetohydrodynamics, thermodynamics, and photochemistry, it is possible to obtain a high resolution view of ultraviolet (UV) fields and their effects in realistic models of the multiphase interstellar medium. Here, we analyze results from TIGRESS-NCR simulations, which follow both far-UV (FUV) wavelengths, important for photoelectric heating and PAH excitation, and the Lyman continuum (LyC), which photoionizes hydrogen. Considering two models, representing solar neighborhood and inner galaxy conditions, we characterize the spatial distribution and time variation of UV radiation fields, and quantify their correlations with gas. We compare four approximate models for the FUV to simulated values to evaluate alternatives when full ART is infeasible. By convolving FUV radiation with density, we produce mock maps of dust emission. We introduce a method to calibrate mid-IR observations, for example from JWST, to obtain high resolution gas surface density maps. We then consider the LyC radiation field, finding most of the gas exposed to this radiation to be in ionization-recombination equilibrium and to have a low neutral fraction. Additionally, we characterize the ionization parameter as a function of environment. Using a simplified model of the LyC radiation field, we produce synthetic maps of emission measure (EM). We show that the simplified model can be used to extract an estimate of the neutral fraction of the photoionized gas and mean free path of ionizing radiation from observed EM maps in galaxies.
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