On the dust geometry in radio-loud active galactic nuclei
  We use photometric and spectroscopic infrared observations obtained with the
Spitzer Space Telescope of 12 radio-loud active galactic nuclei (AGN) to
investigate the dust geometry. Our approach is to look at the change of the
infrared spectral energy distribution (SED) and the strength of the 10 micron
silicate feature with jet viewing angle. We find that (i) a combination of
three or four blackbodies fits well the infrared SED; (ii) the sources viewed
closer to the jet axis appear to have stronger warm (~300 - 800 K) and cold
(~150 - 250 K) dust emissions relative to the hot component; and (iii) the
silicate features are always in emission and strongly redshifted. We test
clumpy torus models and find that (i) they approximate well the mid-infrared
part of the SED, but significantly underpredict the fluxes at both near- and
far-infrared wavelengths; (ii) they can constrain the dust composition (in our
case to that of the standard interstellar medium); (iii) they require
relatively large (~10%-20% the speed of light) redward displacements; and (iv)
they give robust total mass estimates, but are insensitive to the assumed
geometry.
