HST and Spitzer point source detection and optical extinction in
  powerful narrow-line radio galaxies
  We present the analysis of infrared HST and Spitzer data for a sample of 13
FRII radio galaxies at 0.03<z<0.11 that are classified as narrow-line radio
galaxies (NLRG). In the context of the unified schemes for active galactic
nuclei (AGN), our direct view of the AGN in NLRG is impeded by a parsec-scale
dusty torus structure. Our high resolution infrared observations provide new
information about the degree of extinction induced by the torus, and the
incidence of obscured AGN in NLRG.
  We find that the point-like nucleus detection rate increases from 25 per cent
at 1.025$\mu$m, to 80 per cent at 2.05$\mu$m, and to 100 per cent at 8.0$\mu$m.
This supports the idea that most NLRG host an obscured AGN in their centre. We
estimate the extinction from the obscuring structures using X-ray, near-IR and
mid-IR data. We find that the optical extinction derived from the 9.7$\mu$m
silicate absorption feature is consistently lower than the extinction derived
using other techniques. This discrepancy challenges the assumption that all the
mid-infrared emission of NLRG is extinguished by a simple screen of dust at
larger radii. This disagreement can be explained in terms of either weakening
of the silicate absorption feature by (i) thermal mid-IR emission from the
narrow-line region, (ii) non-thermal emission from the base of the radio jets,
or (iii) by direct warm dust emission that leaks through a clumpy torus without
suffering major attenuation.
