Polarization is the next frontier of cosmic microwave background analysis, but its signal is dominated over much of the sky by foregrounds which must be carefully removed. To determine the efficacy of this cleaning, it is necessary to have sensitive tests for residual foreground contamination in polarization sky maps. The dominant Galactic foregrounds introduce a large-scale anisotropy on to the sky, so it makes sense to use a statistic sensitive to overall directionality for this purpose. Here, we adapt the rapidly computable D statistic of Bunn and Scott to polarization data, and demonstrate its utility as a foreground monitor by applying it to the low resolution Wilkinson Microwave Anisotropy Probe 3-yr sky maps. With a thorough simulation of the maps’ noise properties, we find no evidence for contamination in the foreground cleaned sky maps.

Document Type


Publication Date


Publisher Statement

Copyright © 2007 The Authors. This article first appeared in Monthly Notices of the Royal Astronomical Society 381, no. 1 (July 3, 2007): 2-6. doi:10.1111/j.1365-2966.2007.12180.x.

Please note that downloads of the article are for private/personal use only.