A critical challenge in measuring the power spectrum of 21?cm emission from cosmic reionization is compensating for the frequency dependence of an interferometer's sampling pattern, which can cause smooth-spectrum foregrounds to appear unsmooth and degrade the separation between foregrounds and the target signal. In this paper, we present an approach to foreground removal that explicitly accounts for this frequency dependence. We apply the delay transformation introduced in Parsons & Backer to each baseline of an interferometer to concentrate smooth-spectrum foregrounds within the bounds of the maximum geometric delays physically realizable on that baseline. By focusing on delay modes that correspond to image-domain regions beyond the horizon, we show that it is possible to avoid the bulk of smooth-spectrum foregrounds. We map the point-spread function of delay modes to k-space, showing that delay modes that are uncorrupted by foregrounds also represent samples of the three-dimensional power spectrum, and can be used to constrain cosmic reionization. Because it uses only spectral smoothness to differentiate foregrounds from the targeted 21?cm signature, this per-baseline analysis approach relies on spectrally and spatially smooth instrumental responses for foreground removal. For sufficient levels of instrumental smoothness relative to the brightness of interfering foregrounds, this technique substantially reduces the level of calibration previously thought necessary to detect 21?cm reionization. As a result, this approach places fewer constraints on antenna configuration within an array, and in particular, facilitates the adoption of configurations that are optimized for power-spectrum sensitivity. Under these assumptions, we demonstrate the potential for the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21?cm reionization at an amplitude of 10?mK2 near k ~ 0.2 h Mpc–1 with 132 dipoles in 7 months of observing.
展开▼
机译：测量宇宙电离产生的21？cm发射功率谱的一个关键挑战是补偿干涉仪采样模式的频率依赖性，这可能会导致平滑频谱的前景显得不平滑，并降低前景与目标信号之间的距离。在本文中，我们提出了一种前景去除方法，该方法明确考虑了这种频率依赖性。我们将Parsons＆Backer中引入的延迟变换应用于干涉仪的每个基线，以将平滑频谱前景集中在该基线上实际可实现的最大几何延迟的范围内。通过关注与地平线以外的图像域区域相对应的延迟模式，我们表明可以避免大量的平滑光谱前景。我们将延迟模式的点扩展函数映射到k空间，这表明未被前景破坏的延迟模式也表示三维功率谱的样本，并且可以用于约束宇宙离子化。因为它仅使用频谱平滑度来区分前景与目标的21？cm签名，所以这种基于基线的分析方法依赖于频谱和空间上平滑的仪器响应来去除前景。为了相对于干扰前景的亮度具有足够的仪器平滑度，该技术将大大降低以前认为是检测21？cm离子化所必需的校准水平。结果，该方法对阵列内的天线配置施加了较少的约束，并且特别地，其促进了针对功率频谱灵敏度优化的配置的采用。在这些假设下，我们证明了探测电离时代的精密阵列（PAPER）在观测7个月内以132偶极在k〜0.2 h Mpc-1附近以10？mK2的振幅检测10？mK2时具有21？cm电离的潜力。 。
展开▼
