Polarization of the WMAP Point Sources

Abstract

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. Estimated polarized fluxes P < 400 mJy at 23 GHz were found to be severely affected by the Eddington bias. The corresponding polarized flux limit for Planck/LFI at 30 GHz, obtained via realistic simulations, is 300 mJy. We have also obtained statistical estimates of, or upper limits to the mean polarization degrees of bright WMAP sources at 23, 33, 41, and 61 GHz, finding that they are of a few percent.

10 pages, 6 figures. Accepted for publication in ApJ

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• A 3.5mm Polarimetric Survey of Radio-loud Active Galactic Nuclei
• The impact of polarized extragalactic radio sources on the detection of CMB anisotropies in polarization
• The Atacama Cosmology Telescope: Two-season ACTPol Extragalactic Point Sources and their Polarization properties
• Statistical properties of polarized radio sources at high frequency and their impact on CMB polarization measurements
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• Forecasting Polarized Radio Sources for CMB observations
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• Statistics of the fractional polarisation of compact radio sources in Planck maps
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• Characterization of the polarized synchrotron emission from Planck and WMAP data
• Average fractional polarization of extragalactic sources at Planck frequencies
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• Cosmological Particle Production and Pairwise Hotspots on the CMB
• A multifrequency method based on the Matched Multifilter for the detection of point sources in CMB maps
• The polarimetric multi-frequency radio sources properties
• The Planck On-Flight Forecaster (POFF)
• Compact source detection in multi-channel microwave surveys: from SZ clusters to polarized sources
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