MasQU: Finite Differences on Masked Irregular Stokes Q,U Grids

Understand

The detection of B-mode polarization in the CMB is one of the most important outstanding tests of inflationary cosmology.

• One of the necessary steps for extracting polarization information in the CMB is reducing contamination from so-called "ambiguous modes" on a masked sky, which contain leakage from the larger E-mode signal.
• This can be achieved by utilising derivative operators on the real-space Stokes Q and U parameters.
• This paper presents an algorithm and a software package to perform this procedure on the nearly full sky, i.e., with projects such as the Planck Surveyor and future satellites in mind; in particular, the package can perform finite differences on masked, irregular grids and is applied to a semi-regular spherical pixellization, the HEALPix grid.