Polarization of the WMAP Point Sources

Understand

The detection of polarized sources in the WMAP 5-year data is a very difficult task.

• The maps are dominated by instrumental noise and only a handful of sources show up as clear peaks in the Q and U maps.
• Optimal linear filters applied at the position of known bright sources detect with a high level of significance a polarized flux P from many more sources, but estimates of P are liable to biases.
• Using a new technique, named the "filtered fusion technique", we have detected in polarization, with a significance level greater than 99.99% in at least one WMAP channel, 22 objects, 5 of which, however, do not have a plausible low radio frequency counterpart and are therefore doubtful.