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arXiv 1902.08706astro-ph.CO
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非高斯性对再电离期21厘米功率谱观测误差协方差的影响

The impact of non-Gaussianity on the error covariance for observations of the Epoch of Reionization 21-cm power spectrum

Abinash Kumar Shaw, Somnath Bharadwaj, Rajesh Mondal

备注：
15 pages, 10 figures, Accepted for publication in MNRAS
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摘要：

最近的模拟表明，再电离时期（EoR）21厘米信号是固有的非高斯，其中21厘米功率谱（PS）的误差协方差矩阵$\mathbf{C}_{ij}$包含三谱的贡献，如果信号是高斯的，将不存在。使用模拟的分箱功率谱和三谱，在这里，我们提出了一种方法，将这些与基线分布和系统噪声与任何无线电干涉阵列的观测误差预测。在这里，我们考虑即将到来的SKA-Low。非高斯性增强了引入相对于高斯预测的正偏差$Δ$的误差。$Δ$随观测时间增加而增加，$t_{\rm obs}$随着误差接近宇宙方差而饱和。考虑到$t_{\rm obs}=1024$小时，其中$5 σ$检测是可能的，在所有的红移$7 \le z \le 13$，在前景的情况下，我们发现，偏差是重要的，在小$k$，我们有$Δ\sim 40-100 \%$在$k~\sim 0.04 ~{\rm Mpc}^{-1}$的一些红移，也在中间$k \, (\sim 0.4 ~{\rm Mpc}^{-1})$，我们有$Δ\sim 200 \%$在$z=7$。非高斯性还引入了不同$k$箱中的误差之间的相关性，并且我们发现了相关性和与相关系数值跨越$-0.4 \le r_{ij} \le 0.8$的关系。除了前景楔形，$Δ$在$z=7$上仍然很重要（$> 50\%$）。我们的结论是，非高斯性作出了重大贡献的错误，这是重要的，在未来的仪器，旨在实现高灵敏度测量的EoR 21厘米PS的背景下。

英文摘要：

Recent simulations show the Epoch of Reionization (EoR) 21-cm signal to be inherently non-Gaussian whereby the error covariance matrix $\mathbf{C}_{ij}$ of the 21-cm power spectrum (PS) contains a trispectrum contribution that would be absent if the signal were Gaussian. Using the binned power spectrum and trispectrum from simulations, here we present a methodology for incorporating these with the baseline distribution and system noise to make error predictions for observations with any radio-interferometric array. Here we consider the upcoming SKA-Low. Non-Gaussianity enhances the errors introducing a positive deviation $Δ$ relative to the Gaussian predictions. $Δ$ increases with observation time $t_{\rm obs}$ and saturates as the errors approach the cosmic variance. Considering $t_{\rm obs}=1024$ hours where a $5 σ$ detection is possible at all redshifts $7 \le z \le 13$, in the absence of foregrounds we find that the deviations are important at small $k$ where we have $Δ\sim 40-100 \%$ at $k~\sim 0.04 ~{\rm Mpc}^{-1}$ for some of the redshifts and also at intermediate $k \, (\sim 0.4 ~{\rm Mpc}^{-1})$ where we have $Δ\sim 200 \%$ at $z=7$. Non-Gaussianity also introduces correlations between the errors in different $k$ bins, and we find both correlations and anticorrelations with the correlation coefficient value spanning $-0.4 \le r_{ij} \le 0.8$. Incorporating the foreground wedge, $Δ$ continues to be important ($> 50\%$) at $z=7$. We conclude that non-Gaussianity makes a significant contribution to the errors and this is important in the context of the future instruments that aim to achieve high-sensitivity measurements of the EoR 21-cm PS.

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