用小波散射变换检测再电离过程中21厘米信号的非高斯性
Detecting the non-Gaussianity of the 21-cm signal during reionisation with the Wavelet Scattering Transform
摘要：
探测星系际介质中中性氢的21厘米超精细跃迁是我们了解驱动再电离时代（EoR）的天体物理过程的最佳探测器。用于检测该21 cm信号的主要手段是通过使用21 cm功率谱（PS）的空间波动的统计测量。然而，21-cm信号是非高斯的，这意味着仅测量高斯波动的PS对于表征所有可用信息而言是次优的。即将到来的平方公里阵列（SKA）将在100度$.^{2}$上进行1000小时的深度观测，专门用于恢复21厘米信号的直接图像。在这项工作中，我们使用小波散射变换（WST）直接从这些二维图像的21厘米信号提取非高斯信息。WST的主要优点是其相对于用于测量非高斯信息的统计噪声的稳定性，不像统计噪声发散的双谱。我们介绍了一种新的方法，以隔离这种非高斯信息从模拟21厘米图像，并证明其检测在150（177）MHz（$z\sim8.5$和$\sim7$）的基准模型与$\sim$ 5~（8）假设完美的前景消除和$\sim2$ ~（3）假设前景楔回避信噪比。
英文摘要：
Detecting the 21-cm hyperfine transition from neutral hydrogen in the intergalactic medium is our best probe for understanding the astrophysical processes driving the Epoch of Reionisation (EoR). The primary means for a detection of this 21-cm signal is through a statistical measurement of the spatial fluctuations using the 21-cm power spectrum (PS). However, the 21-cm signal is non-Gaussian meaning the PS, which only measures the Gaussian fluctuations, is sub-optimal for characterising all of the available information. The upcoming Square Kilometre Array (SKA) will perform a deep, 1000 hr observation over 100 deg$.^{2}$ specifically designed to recover direct images of the 21-cm signal. In this work, we use the Wavelet Scattering Transform (WST) to extract the non-Gaussian information directly from these two-dimensional images of the 21-cm signal. The key advantage of the WST is its stability with respect to statistical noise for measuring non-Gaussian information, unlike the bispectrum whose statistical noise diverges. We introduce a novel method to isolate this non-Gaussian information from mock 21-cm images and demonstrate its detection at 150 (177)~MHz ($z\sim8.5$ and $\sim7$) for a fiducial model with signal-to-noise of $\sim$5~(8) assuming perfect foreground removal and $\sim2$~(3) assuming foreground wedge avoidance.
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