The 1.6 micron near infrared nuclei of 3C radio galaxies: Jets, thermal
  emission or scattered light?
  Using HST NICMOS 2 observations we have measured 1.6-micron near infrared
nuclear luminosities of 100 3CR radio galaxies with z<0.3, by modeling and
subtracting the extended emission from the host galaxy. We performed a
multi-wavelength statistical analysis (including optical and radio data) of the
properties of the nuclei following classification of the objects into FRI and
FRII, and LIG (low-ionization galaxies), HIG (high-ionization galaxies) and BLO
(broad-lined objects) using the radio morphology and optical spectra,
respectively. The correlations among near infrared, optical, and radio nuclear
luminosity support the idea that the near infrared nuclear emission of FRIs has
a non-thermal origin. Despite the difference in radio morphology, the
multi-wavelength properties of FRII LIG nuclei are statistically
indistinguishable from those of FRIs, an indication of a common structure of
the central engine. All BLOs show an unresolved near infrared nucleus and a
large near infrared excess with respect to FRII LIGs and FRIs of equal radio
core luminosity. This requires the presence of an additional (and dominant)
component other than the non-thermal light. Considering the shape of their
spectral energy distribution, we ascribe the origin of their near infrared
light to hot circumnuclear dust. A near infrared excess is also found in HIGs,
but their nuclei are substantially fainter than those of BLO. This result
indicates that substantial obscuration along the line-of-sight to the nuclei is
still present at 1.6 micron. Nonetheless, HIGs nuclei cannot simply be
explained in terms of dust obscuration: a significant contribution from light
reflected in a circumnuclear scattering region is needed to account for their
multiwavelength properties.
