Smoothing methods comparison for CMB E- and B-mode separation

• Published in: Research in astronomy and astrophysics Vol. 16; no. 4; pp. 55 - 62
• Main Authors: Wang, Yi-Fan, Wang, Kai, Zhao, Wen
• Format: Journal Article
• Language: English
• Published: National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing 01.04.2016
• Subjects: Astronomy; CMB; Cosmic microwave background; cosmic microwave background radiation; Errors; Image processing; Leakage; Masks; Mathematical models; polarization; Separation; Smoothing; statistics; 分离方法; 宇宙微波背景辐射; 平滑方法; 数值误差; 早期宇宙; 电子商务
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/16/4/059

The anisotropies of the B-mode polarization in the cosmic microwave background radiation play a crucial role in the study of the very early Universe. However, in real observations, a mixture of the E- mode and B-mode can be caused by partial sky surveys, which must be separated before being applied to a cosmological explanation. The separation method developed by Smith （2006） has been widely adopted, where the edge of the top-hat mask should be smoothed to avoid numerical errors. In this paper, we compare three different smoothing methods and investigate leakage residuals of the E-B mixture. We find that, if less information loss is needed and a smaller region is smoothed in the analysis, the sin- and cos-smoothing methods are better. However, if we need a cleanly constructed B-mode map, the larger region around the mask edge should be smoothed. In this case, the Gaussian-smoothing method becomes much better. In addition, we find that the leakage caused by numerical errors in the Gaussian-smoothing method is mostly concentrated in two bands, which is quite easy to reduce for further E-B separations.