论文标题
仪器响应在21 cm EOR功率谱网格分析中的作用
The Role of the Instrumental Response in 21 cm EoR Power Spectrum Gridding Analyses
论文作者
论文摘要
通过网格技术或空间傅立叶空间中的直方图实现了通过无线电干涉仪测量的天空亮度的重建。对于回电时期（EOR）21 cm功率谱测量，如其他作品中所探讨的那样，需要极高水平的网格分辨率来减少光谱污染。但是，傅立叶空间扩散函数或内核的形状的作用在重建的功率谱也有后果。我们将仪器的默奇森广场阵列（MWA）梁分解为一系列高斯人，并模拟有限核量表的效果以及在网格/脱水中的不同形状，以进行最佳的地图进行分析。对于MWA，我们发现内核必须延伸至最大值的0.001--0.0001％，以便使用前景回避测量EOR。此需求取决于光束形状，紧凑的内核需要以较小的污染水平，以较小的误差为代价。但是，无论内核的形状如何，都使用像素化脱粒结果的简单校准都无法恢复由于像素分辨率引起的灾难性误差所致。包括不透明的地平线，带有广场梁的地平线也会通过梁（横梁） - Horizon相互作用引起严重的光谱污染，该横梁相互作用在傅立叶空间中产生无限扩展的核，这不能很好地表示。因此，我们的结果表明，通过脱粒模型进行的简单校准以及为极端广阔的仪器制作的最佳图是不可行的。
Reconstruction of the sky brightness measured by radio interferometers is typically achieved through gridding techniques, or histograms in spatial Fourier space. For Epoch of Reionisation (EoR) 21 cm power spectrum measurements, extreme levels of gridding resolution are required to reduce spectral contamination, as explored in other works. However, the role of the shape of the Fourier space spreading function, or kernel, also has consequences in reconstructed power spectra. We decompose the instrumental Murchison Widefield Array (MWA) beam into a series of Gaussians and simulate the effects of finite kernel extents and differing shapes in gridding/degridding for optimal map making analyses. For the MWA, we find that the kernel must extend out to 0.001--0.0001% of the maximum value in order to measure the EoR using foreground avoidance. This requirement changes depending on beam shape, with compact kernels requiring far smaller extents for similar contamination levels at the cost of less-optimal errors. However, simple calibration using pixelated degridding results, regardless of shape of the kernel, cannot recover the EoR due to catastrophic errors caused by the pixel resolution. Including an opaque horizon with widefield beams also causes significant spectral contamination via a beam--horizon interaction that creates an infinitely extended kernel in Fourier space, which cannot be represented well. Thus, our results indicate that simple calibration via degridded models and optimal map making for extreme widefield instrumentation are not feasible.
