在全球21厘米测量的平均光谱中引起吸收轮廓的地平面反射器--及其对EDGES的可能应用
A Ground Plane Artifact that Induces an Absorption Profile in Averaged Spectra from Global 21-cm Measurements - with Possible Application to EDGES
摘要：
目前的大多数全球21厘米实验包括地面屏幕，有助于减轻来自地球的影响。在本文中，我们报告一个可能的系统性的工件内的地平面，可能会产生广泛的吸收功能，在这些实验观察到的光谱。使用解析近似和数值模拟，伪影的起源及其对天空平均光谱的影响进行了描述。公开发布的EDGES数据集，其中一个78 MHz的吸收功能，最近建议，用于探测潜在的存在接地平面谐振。虽然EDGES频谱缺乏噪声水平使得传统的拟合优度统计无法实现，但均方根残差可用于评估在类似情况下执行的相对拟合优度。使用具有简单2项前景和三个腔模共振的模型拟合EDGES光谱与EDGES团队使用的由5项前景和平坦高斯信号组成的模型拟合相同的光谱进行比较。与物理激励共振和经验平坦高斯模型的拟合分别具有20.8 mK（11个参数）和24.5 mK（9个参数）的均方根残差，这使我们能够得出结论，接地层共振构成了对EDGES数据的另一种合理解释。
英文摘要：
Most of the current Global 21-cm experiments include ground screens that help moderate effects from the Earth. In this paper, we report on a possible systematic artifact within the ground plane that may produce broad absorption features in the spectra observed by these experiments. Using analytical approximations and numerical modeling, the origin of the artifact and its impact on the sky-averaged spectrum are described. The publicly released EDGES dataset, from which a 78 MHz absorption feature was recently suggested, is used to probe for the potential presence of ground plane resonances. While the lack of a noise level for the EDGES spectrum makes traditional goodness-of-fit statistics unattainable, the rms residual can be used to assess the relative goodness of fits performed under similar circumstances. The fit to the EDGES spectrum using a model with a simple 2-term foreground and three cavity-mode resonances is compared to a fit to the same spectrum with a model used by the EDGES team consisting of a 5-term foreground and a flattened Gaussian signal. The fits with the physically motivated resonance and empirical flattened Gaussian models have rms residuals of 20.8 mK (11 parameters) and 24.5 mK (9 parameters), respectively, allowing us to conclude that ground plane resonances constitute another plausible explanation for the EDGES data.
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