The Nature of the Near-IR Core Source in 3C 433
  We report the analysis of near-infrared imaging, polarimetric and
spectroscopic observations of the powerful radio galaxy 3C433, obtained with
the HST and UKIRT telescopes. The high spatial resolution of HST allows us to
study the near-nuclear regions of the galaxy (<1 kpc). In line with previous
observations, we find that 3C433 has an unresolved core source that is detected
in all near-IR bands, but dominates over the host galaxy emission at 2.05 um.
Our analysis reveals: (1) the presence of a dust lane aligned close to
perpendicular (PA$=70\pm5\degr$) to the inner radio jet axis
(PA$=-12\pm2\degr$); (2) a steep slope to the near-IR SED ($\alpha=5.8\pm0.1$;
F$_{\nu}\propto\nu^{-\alpha}$); (3) an apparent lack of broad permitted
emission lines at near-IR wavelengths, in particular the absence of a broad
Pa$\alpha$ emission line; and (4) high intrinsic polarization for the
unresolved core nuclear source ($8.6\pm1$ per cent), with an E-vector
perpendicular (PA=$83.0\pm 2.3\degr$) to the inner radio jet. Using five
independent techniques we determine an extinction to the compact core source in
the range 3<A_V<67 mag. An analysis of the long wavelength SED rules out a
synchrotron origin for the high near-IR polarization of the compact core
source. Therefore, scattering and dichroic extinction are plausible polarizing
mechanisms, although in both of these cases the broad permitted lines from the
AGN are required to have a width >10^4 km/s (FWHM) to escape detection in our
near-IR spectrum. Dichroic extinction is the most likely polarization mechanism
because it is consistent with the various available extinction estimates. In
this case, a highly ordered, coherent toroidal magnetic field must be present
in the obscuring structure close to the nucleus.
