AI 中文总结
本研究利用CROC模拟计算CMB光深角功率谱，分解电子密度场量化两类涨落的贡献，结合低红移解析估计，发现密度涨落对光深功率贡献显著，提示未来解读需考虑该因素。
AI 中文摘要
汤姆逊光深的空间涨落承载着宇宙再电离非均匀特性的信息。我们利用由5组Cosmic Reionization on Computers（CROC，计算机宇宙再电离）辐射流体动力学模拟构建的过去光锥，计算了光深角功率谱$C_\ell^{ττ}$。通过将电子密度场分解为斑块组分与密度组分，我们量化了电离分数涨落和重子密度涨落对光深各向异性的各自贡献。由于模拟终止于红移$z\approx5$，我们采用完全电离的低红移贡献的解析估计，对再电离时期的信号进行补充。研究发现，在多数角尺度上，重子密度涨落在高红移信号中占主导地位，而在我们所考虑的全部多极矩范围内，累积的低红移贡献均超过高红移信号。我们的结果表明，很大一部分光深功率并非唯一对应于再电离的形态特征，这意味着未来对$C_\ell^{ττ}$的解读除了斑块化电离之外，还必须考虑密度贡献。
英文摘要
Spatial fluctuations in the Thomson optical depth encode information about the inhomogeneous nature of cosmic reionization. We compute the optical-depth angular power spectrum, $C_\ell^{ττ}$, using past lightcones constructed from five Cosmic Reionization on Computers (CROC) radiation-hydrodynamical simulations. By decomposing the electron-density field into patchy and density components, we quantify the separate contributions of ionization-fraction and baryon-density fluctuations to the optical-depth anisotropy. Because the simulations end at $z\approx5$, we supplement the reionization-era signal with an analytic estimate of the fully ionized low-redshift contribution. We find that baryon-density fluctuations dominate the high-redshift signal over most angular scales, while the accumulated low-redshift contribution exceeds the high-redshift signal across the full multipole range considered. Our results demonstrate that a significant fraction of the optical-depth power is not uniquely associated with reionization morphology, implying that future interpretations of $C_\ell^{ττ}$ must account for the density contribution in addition to patchy ionization.
