Flat-Sky Pseudo-Cls Analysis for Weak Gravitational Lensing
Flat-Sky Pseudo-Cls Analysis for Weak Gravitational Lensing
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DOI：
10.1093/mnras/sty1412
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发表时间：
2016-12
影响因子：
4.8
通讯作者：
M. Asgari;A. Taylor;B. Joachimi;T. Kitching
中科院分区：
文献类型：
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作者：
M. Asgari;A. Taylor;B. Joachimi;T. Kitching
我们研究了基于伪cl （PCl）技术的平天实现的弱透镜功率谱估计器的使用，其中掩模剪切场被变换而不考虑天空的掩模区域。这种掩蔽混合了功率、e -收敛和b -模式。为了研究正演模拟和全天功率谱恢复的准确性，我们考虑了大面积测量几何形状、由于恒星和视场间隙的棋盘模型造成的小尺度掩蔽。大面积测量几何的功率谱是稀疏采样和高度振荡的，这使得建模存在问题。相反，我们使用模拟场推导出大面积掩模偏置的总体校准。小面积星形掩模的影响可以精确地纠正，而棋盘掩模具有振荡和尖尖的行为，导致百分比偏差。屏蔽场的消隐导致偏差增加和信息丢失。我们发现，我们可以构建原始pcl的无偏正演模型，并将高斯和对数正态分布的剪切场的全天收敛功率恢复到精度在几个百分点以内。使用费雪矩阵形式将其传播到宇宙学参数，我们发现我们可以对每角分30个星系的1200度范围内的调查参数进行无偏估计，超过这个范围，偏差百分比就会大于统计精度。这意味着平天的PCl分析对于当前的调查是准确的，但类似欧几里得的调查将需要更高的精度。
We investigate the use of estimators of weak lensing power spectra based on a flat-sky implementation of the Pseudo-Cl (PCl) technique, where the masked shear field is transformed without regard for masked regions of sky. This masking mixes power, and E-convergence and B-modes. To study the accuracy of forward-modelling and full-sky power spectrum recovery we consider both large-area survey geometries, and small-scale masking due to stars and a checkerboard model for field-of-view gaps. The power spectrum for the large-area survey geometry is sparsely-sampled and highly oscillatory, which makes modelling problematic. Instead, we derive an overall calibration for large-area mask bias using simulated fields. The effects of small-area star masks can be accurately corrected for, while the checkerboard mask has oscillatory and spiky behaviour which leads to percent biases. Apodisation of the masked fields leads to increased biases and a loss of information. We find that we can construct an unbiased forward-model of the raw PCls, and recover the full-sky convergence power to within a few percent accuracy for both Gaussian and lognormal-distributed shear fields. Propagating this through to cosmological parameters using a Fisher-Matrix formalism, we find we can make unbiased estimates of parameters for surveys up to 1,200 deg$^2$ with 30 galaxies per arcmin$^2$, beyond which the percent biases become larger than the statistical accuracy. This implies a flat-sky PCl analysis is accurate for current surveys but a Euclid-like survey will require higher accuracy.