Biases in the polarization position angles in the NRAO-VLA sky survey point source catalogue

R. A. Battye, I. W A Browne, N. Jackson

    Research output: Contribution to journalArticlepeer-review


    We have examined the statistics of the polarization position angles determined for point sources in the NRAO-VLA Sky Survey (NVSS), and find that there is a statistically significant bias towards angles which are multiples of 45°. The formal probability that the polarization angles are drawn from a uniform distribution is exponentially small. When the sample of those NVSS sources with polarizations detected with a signal-to-noise ratio ≥3 is split either around the median polarized flux density or the median fractional polarization, the effect appears to be stronger for the more highly polarized sources. Regions containing strong sources and regions at low-Galactic latitudes are not responsible for the non-uniform distribution of position angles. We identify clean bias as the probable cause of the dominant effect, coupled with small multiplicative and additive offsets on each of the Stokes parameters. Our findings have implications for the extraction of science, such as information concerning galactic magnetic fields, from large-scale polarization surveys. © 2007 RAS.
    Original languageEnglish
    Pages (from-to)274-282
    Number of pages8
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number1
    Publication statusPublished - Mar 2008


    • Galaxies: active
    • Polarization
    • Surveys


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