全球21厘米信号分析假设的制定和批判性检验：如何避免单谱拟合中可能出现的假波谷
Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits
摘要：
全球21 cm信号分析所固有的假设很少被描述。在本文中，我们制定了一个一般列表的假设基础上的一个给定的声称检测的全球21厘米的信号。然后，我们为两种不同的分析指定了这些假设的形式：1）由EDGES团队执行的一种，显示了他们从天空前景中单独建模的亮度温度吸收槽，2）一种新的，所谓的最小假设分析（MAA），它使信号的最保守假设成为可能。我们显示适合使用各种波束加权的前景模拟从没有添加信号的边缘纬度的边缘分析。根据所使用的光束，这些模拟产生大的假槽，由于前景模型的无效性来描述光束色度和天空中的银河平面的形状的组合，其残差被捕获的特设平坦高斯信号模型。另一方面，MAA提供了强大的拟合，包括许多光谱在不同的时间箱，并允许任何可能的21厘米光谱精确建模。我们目前的不确定性水平和示例信号重建发现与MAA不同数量的时间仓。有了足够的时间仓，就可以用噪声电平的$<10$倍的MAA确定真正的21 cm信号。
英文摘要：
The assumptions inherent to global 21-cm signal analyses are rarely delineated. In this paper, we formulate a general list of suppositions underlying a given claimed detection of the global 21-cm signal. Then, we specify the form of these assumptions for two different analyses: 1) the one performed by the EDGES team showing an absorption trough in brightness temperature that they modeled separately from the sky foreground and 2) a new, so-called Minimum Assumption Analysis (MAA), that makes the most conservative assumptions possible for the signal. We show fits using the EDGES analysis on various beam-weighted foreground simulations from the EDGES latitude with no signal added. Depending on the beam used, these simulations produce large false troughs due to the invalidity of the foreground model to describe the combination of beam chromaticity and the shape of the Galactic plane in the sky, the residuals of which are captured by the ad hoc flattened Gaussian signal model. On the other hand, the MAA provides robust fits by including many spectra at different time bins and allowing any possible 21-cm spectrum to be modeled exactly. We present uncertainty levels and example signal reconstructions found with the MAA for different numbers of time bins. With enough time bins, one can determine the true 21-cm signal with the MAA to $<10$ times the noise level.
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