From top-hat masking to smooth transitions: P-filter and its application to polarized microwave sky maps

Hao Liu, James Creswell, Sebastian von Hausegger, Pavel Naselsky
2019 Journal of Cosmology and Astroparticle Physics  
In CMB science, the simplest idea to remove a contaminated sky region is to multiply the sky map with a mask that is 0 for the contaminated region and 1 elsewhere, which is also called a top-hat masking. Although it is easy to use, such top-hat masking is known to suffer from various leakage problems. Therefore, we want to extend the top-hat masking to a series of semi-analytic functions called the P-filters. Most importantly, the P-filters can seamlessly realize the core idea of masking in CMB
more » ... science, and, meanwhile, guarantee continuity up to the first derivative everywhere. The P-filters can significantly reduce many leakage problems without additional cost, including the leakages due to low-, high-, and band-pass filtering, and the E-to-E, B-to-B, B-to-E, and E-to-B leakages. The workings of the P-filter are illustrated by using the WMAP and Planck polarization sky maps. By comparison to the corresponding WMAP/Planck masks, we show that the P-filter performs much better than top-hat masking, and meanwhile, has the potential to supersede the principal idea of masking in CMB science. Compared to mask apodization, the P-filter is "outward", that tends to make proper use of the region that was marked as 0; whereas apodization is "inward", that always kills more signal in the region marked as 1.
doi:10.1088/1475-7516/2019/05/003 fatcat:zypupdld3zd7zkgkjw2i2yhe4m