The Q/U Imaging Experiment: Polarization Measurements of Radio Sources at 43 and 95 GHz

K M Huffenberger, D Araujo, C Bischoff, I Buder, Y Chinone, K Cleary, A Kusaka, R Monsalve, S K Næss, L B Newburgh, R Reeves, T M Ruud, I K Wehus, J T L Zwart, C Dickinson, H K Eriksen, T Gaier, J O Gundersen, M Hasegawa, M HazumiA D Miller, S J E Radford, A C S Readhead, S T Staggs, O Tajima, K L Thompson, QUIET Collaboration

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    We present polarization measurements of extragalactic radio sources observed during the cosmic microwave background polarization survey of the Q/U Imaging Experiment (QUIET), operating at 43 GHz (Q-band) and 95 GHz (W-band). We examine sources selected at 20 GHz from the public, >40 mJy catalog of the Australia Telescope (AT20G) survey. There are ˜480 such sources within QUIET’s four low-foreground survey patches, including the nearby radio galaxies Centaurus A and Pictor A. The median error on our polarized flux density measurements is 30-40 mJy per Stokes parameter. At signal-to-noise ratio > 3 significance, we detect linear polarization for seven sources in Q-band and six in W-band; only 1.3 ± 1.1 detections per frequency band are expected by chance. For sources without a detection of polarized emission, we find that half of the sources have polarization amplitudes below 90 mJy (Q-band) and 106 mJy (W-band), at 95% confidence. Finally, we compare our polarization measurements to intensity and polarization measurements of the same sources from the literature. For the four sources with WMAP and Planck intensity measurements >1 Jy, the polarization fractions are above 1% in both QUIET bands. At high significance, we compute polarization fractions as much as 10%-20% for some sources, but the effects of source variability may cut that level in half for contemporaneous comparisons. Our results indicate that simple models—ones that scale a fixed polarization fraction with frequency—are inadequate to model the behavior of these sources and their contributions to polarization maps.
    Original languageEnglish
    JournalThe Astrophysical Journal
    Publication statusPublished - 2015


    • cosmic background radiation
    • galaxies: active
    • galaxies: individual: Cen A
    • Pict A
    • methods: statistical
    • polarization


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