Detection Thresholds and Bias Correction in Polarized Intensity
  Detection thresholds in polarized intensity and polarization bias correction
are investigated for surveys where the polarization information is obtained
from RM synthesis. Considering unresolved sources with a single rotation
measure, a detection threshold of $8 \sigma_{QU}$ applied to the Faraday
spectrum will retrieve the RM with a false detection rate less than $10^{-4}$,
but polarized intensity is more strongly biased than Ricean statistics suggest.
For a detection threshold of $5 \sigma_{QU}$, the false detection rate
increases to ~4%, depending also on $\lambda^2$ coverage and the extent of the
Faraday spectrum. Non-Gaussian noise in Stokes Q and U due to imperfect imaging
and calibration can be represented by a distribution that is the sum of a
Gaussian and an exponential. The non-Gaussian wings of the noise distribution
increase the false detection rate in polarized intensity by orders of
magnitude. Monte-Carlo simulations assuming non-Gaussian noise in Q and U, give
false detection rates at $8 \sigma_{QU}$ similar to Ricean false detection
rates at $4.9 \sigma_{QU}$.
