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arXiv 1407.6772astro-ph.CO
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使用位置角测试CMB极化数据

Testing CMB polarization data using position angles

Michael Preece, Richard Battye

摘要:

我们考虑一种新的零测试污染,它可以应用于CMB偏振数据,涉及分析的偏振位置角的统计。具体来说,我们将集中使用测量的位置角的直方图来说明这个想法。这样的测试已被用来确定系统的NVSS点源目录的振幅远低于噪音水平。我们探讨了CMB映射中偏振角的统计特性。如果偏振角在像素之间不相关,则误差遵循简单的$\sqrt{N_{pix}}$定律。然而,对于CMB图,情况通常不是这样,因为这些具有相关性,这导致方差的增加,因为独立像素的有效数量减少。然后,我们说明了如何某些类别的系统误差可以导致在这些直方图中非常明显的模式,因此,这些错误可能会被识别使用这种方法。我们讨论了如何将这一想法应用于现实环境中,并对WMAP 7数据进行了初步分析,发现Q和W波段数据中存在系统误差的证据,与Q和U中的恒定偏移一致。

英文摘要:

We consider a novel null test for contamination which can be applied to CMB polarization data that involves analysis of the statistics of the polarization position angles. Specifically, we will concentrate on using histograms of the measured position angles to illustrate the idea. Such a test has been used to identify systematics in the NVSS point source catalogue with an amplitude well below the noise level. We explore the statistical properties of polarization angles in CMB maps. If the polarization angle is not correlated between pixels, then the errors follow a simple $\sqrt{N_{pix}}$ law. However this is typically not the case for CMB maps since these have correlations which result in an increase in the variance since the effective number of independent pixels is reduced. Then we illustrate how certain classes of systematic errors can result in very obvious patterns in these histograms, and thus that these errors could possibly be identified using this method. We discuss how this idea might be applied in a realistic context, and make a preliminary analysis of the WMAP7 data, finding evidence of a systematic error in the Q and W band data, consistent with a constant offset in Q and U.

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