Radio Polarization Properties of Quasars and Active Galaxies at High
  Redshifts
  We present the largest ever sample of radio polarization properties for $z>4$
sources, with 14 sources having significant polarization detections. Using
wideband data from the Karl G. Jansky Very Large Array, we obtained the
rest-frame total intensity and polarization properties of 37 radio sources,
nine of which have spectroscopic redshifts in the range $1 \le z \le 1.4$, with
the other 28 having spectroscopic redshifts in the range $3.5 \le z \le 6.21$.
Fits are performed for the Stokes $I$ and fractional polarization spectra, and
Faraday rotation measures are derived using Rotation measure synthesis and $QU$
fitting. Using archival data of 476 polarized sources, we compare high redshift
($z>3$) source properties to a $15\,$GHz rest-frame luminosity matched sample
of low redshift ($z<3$) sources to investigate if the polarization properties
of radio sources at high redshifts are intrinsically different than those at
low redshift. We find a mean of the rotation measure absolute values, corrected
for Galactic rotation, of $50 \pm 22\,$rad m$^{-2}$ for $z>3$ sources and $57
\pm 4\,$rad m$^{-2}$ for $z<3$. Although there is some indication of lower
intrinsic rotation measures at high-$z$ possibly due to higher depolarization
from the high density environments, using several statistical tests we detect
no significant difference between low and high redshift sources. Larger samples
are necessary to determine any true physical difference.
