The rotation measures of high luminosity sources as seen from the NVSS
  We re-analyse the subset of the Faraday rotation measures data from the NRAO
VLA Sky Survey catalogue for which redshift and spectral index information is
available, in order to better elucidate the relations between these
observables. We split this subset in two based on their radio luminosity, and
find that higher power sources have a systematically higher residual rotation
measure, once the regular field of the Milky Way is subtracted. This rotation
measure stands well above the variances due to the turbulent field of our
Galaxy and measurement errors, contrarily to low power sources. The effect is
more pronounced as the energy threshold becomes more restrictive. If the two
sets are merged one observes an apparent evolution of rotation measure with
redshift, but our analysis shows that this can be interpreted as an artifact of
the different intrinsic properties of brighter sources that are typically
observed at larger distances.
