Near-infrared Hubble Space Telescope polarimetry of a complete sample of
  narrow-line radio galaxies
  We present an analysis of 2.05 $\mu$m Hubble Space Telescope (HST)
polarimetric data for a sample of 13 nearby Fanaroff-Riley type II (FRII) 3CR
radio sources ($0.03<z<0.11$) that are classified as narrow line radio galaxies
(NLRG) at optical wavelengths. We find that the compact cores of the NLRG in
our sample are intrinsically highly polarised in the near-IR ($6 < P_{2.05\mu
m} < 60$ per cent), with the electric-vector (E-vector) perpendicular to the
radio axis in 54 per cent of the sources. The levels of extinction required to
produce near-infrared polarisation by the dichroic extinction mechanism are
consistent with the measured values reported in Ram\'irez et al. (2014),
provided that this mechanism has its maximum efficiency. This consistency
suggests that the nuclear polarisation could be due to dichroic extinction. In
this case, toroidal magnetic fields that are highly coherent would be required
in the circumnuclear tori to align the elongated dust grains responsible for
the dichroic extinction. However, it is not entirely possible to rule out other
polarisation mechanisms (e.g. scattering, synchrotron emission) with our
observations at only one near-IR wavelength. Therefore further polarimetry
observations at mid-IR and radio wavelengths will be required to test whether
all the near-IR polarisation is due to dichroic extinction.
