使用Owens Valley长波长阵列在48 MHz下获得21 cm功率谱
A 21-cm power spectrum at 48 MHz, using the Owens Valley Long Wavelength Array
摘要：
探测黑暗时代的大孔径实验（LEDA）旨在测量宇宙黎明时中性氢的21厘米信号，$z \approx $ 15-30。利用欧文斯谷长波长阵列（OVRO-LWA）的$\approx $ 200 m直径的核心所作的观测，我们提出了一个2-D圆柱空间功率谱的数据在43.1-53.5 MHz（$z_{\rm median}\approx 28$）非相干积分为4小时，和阵列的灵敏度分析。来自前景的功率被定位到$k_\perp, k_\parallel$空间内的“楔形”。在使用包括VirA在内的5个明亮紧凑源校准了Vibrium之后，我们测量了前景楔形之外的$Δ^2(k) \approx 2 \times 10^{12}\ \mathrm{mK}^2$，原则上，未受污染的宇宙学信号将位于前景楔形之外。测量的$Δ^2(k)$是反映热仪器和天空噪声的组合的上限，以及从楔形散射功率的未建模的系统，如将讨论的。通过对频率通道的近配对进行差分校准，我们抑制前景天空结构和系统性，提取热噪声，并使用相干和非相干积分的混合来模拟3000 h观测和$z = $ 16-37的噪声主导的功率谱。对于合适的校准质量，所得噪声水平$Δ^2(k) \approx 100$ mK $^2$（k = 0.3 Mpc $^{-1}$）将足以检测由于早期Ly-$α$和X射线源而引起的21-cm空间功率谱中的峰，如针对一系列理论模型参数所预测的。
英文摘要：
The Large-aperture Experiment to detect the Dark Age (LEDA) was designed to measure the 21-cm signal from neutral hydrogen at Cosmic Dawn, $z \approx $15-30. Using observations made with the $\approx $ 200 m diameter core of the Owens Valley Long Wavelength Array (OVRO-LWA), we present a 2-D cylindrical spatial power spectrum for data at 43.1-53.5 MHz ($z_{\rm median}\approx 28$) incoherently integrated for 4 hours, and an analysis of the array sensitivity. Power from foregrounds is localized to a "wedge" within $k_\perp, k_\parallel$ space. After calibration of visibilities using 5 bright compact sources including VirA, we measure $Δ^2(k) \approx 2 \times 10^{12}\ \mathrm{mK}^2$ outside the foreground wedge, where an uncontaminated cosmological signal would lie, in principle. The measured $Δ^2(k)$ is an upper limit that reflects a combination of thermal instrumental and sky noise, and unmodelled systematics that scatter power from the wedge, as will be discussed. By differencing calibrated visibilities for close pairs of frequency channels, we suppress foreground sky structure and systematics, extract thermal noise, and use a mix of coherent and incoherent integration to simulate a noise-dominated power spectrum for a 3000 h observation and $z = $16-37. For suitable calibration quality, the resulting noise level, $Δ^2(k) \approx 100$ mK$^2$ (k = 0.3 Mpc$^{-1}$), would be sufficient to detect peaks in the 21-cm spatial power spectrum due to early Ly-$α$ and X-ray sources, as predicted for a range of theoretical model parameters.
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