标题： 建模银河前景和波束色度以用于全球21厘米宇宙学 显示英文标题

标题： Modelling the Galactic Foreground and Beam Chromaticity for Global 21-cm Cosmology

摘要： 为了表征和建模用于全球21厘米信号实验的束加权前景，我们提出了一种结合银河光谱指数和天空亮度温度的分析模型与模拟具有各种角依赖性和光谱依赖性以及指向的束的观测模型的方法，以生成基特征向量。每种组合都会产生独特的束加权前景。通过使用奇异值分解（SVD）生成拟合每个前景模型的特征向量，我们研究了束加权前景成分变化的影响。我们发现，对于建模无色、各向同性的束（理想情况）的特征向量几乎相同，无论使用的未加权前景模型是什么，并且实际上与基于多项式的模型无法区分。然而，当各向异性、有色束加权前景时，会在前景的空间和光谱结构之间引入耦合，使特征向量偏离多项式模型，并导致基底对束（色散性、模式、指向）和前景（光谱指数、天空亮度温度图）精确特征的依赖性。我们发现束对特征向量的影响大于前景模型。任何不考虑其畸变的模型可能会在六参数、单谱拟合中产生大约$\sim 10$-$10^3$开尔文的RMS不确定性。然而，如果直接使用SVD和训练集将束纳入其中，则所得特征向量可达到毫开尔文级的不确定性。给定足够详细的天空描述，我们的方法可以应用于任何特定实验，只要束得到了适当表征，以便生成准确的束加权前景模型。 显示英文摘要

摘要： In order to characterize and model the beam-weighted foreground for global 21-cm signal experiments, we present a methodology for generating basis eigenvectors that combines analytical and observational models of both the galactic spectral index and sky brightness temperature with simulations of beams having various angular and spectral dependencies and pointings. Each combination creates a unique beam-weighted foreground. By generating eigenvectors to fit each foreground model using Singular Value Decomposition (SVD), we examine the effects of varying the components of the beam-weighted foreground. We find that the eigenvectors for modelling an achromatic, isotropic beam -- the ideal case -- are nearly identical regardless of the unweighted foreground model used, and are practicably indistinguishable from polynomial-based models. When anisotropic, chromatic beams weight the foreground, however, a coupling is introduced between the spatial and spectral structure of the foreground which distorts the eigenvectors away from the polynomial models and induces a dependence of the basis upon the exact features of the beam (chromaticity, pattern, pointing) and foreground (spectral index, sky brightness temperature map). We find that the beam has a greater impact upon the eigenvectors than foreground models. Any model which does not account for its distortion may produce RMS uncertainties on the order of $\sim 10$ - $10^3$ Kelvin for six-parameter, single spectrum fits. If the beam is incorporated directly using SVD and training sets, however, the resultant eigenvectors yield milli-Kelvin level uncertainties. Given a sufficiently detailed description of the sky, our methodology can be applied to any particular experiment with a suitably characterized beam for the purpose of generating accurate beam-weighted foreground models.