The dusty heart of nearby active galaxies -- II. From clumpy torus
  models to physical properties of dust around AGN
  The dusty environments (= "dust tori'') of AGN are now in reach of
observations. Following our paper I on ground-based mid-IR spectro-photometry
(H\"onig et al. 2010), we present an upgrade to our radiative transfer model of
3-dimensional clumpy dust tori. The upgrade with respect to H\"onig et al.
(2006) concerns an improved handling of the diffuse radiation field in the
torus which is approximated by a statistical approach. The models are presented
as tools to translate classical and interferometric observations into
characteristic properties of the dust distribution. We compare model SEDs for
different chemical and grain-size compositions of the dust and find that clouds
with standard ISM dust and optical depth tau_V~50 appear in overall agreement
with observed IR SEDs. By studying parameter dependencies, it is shown that
type 1 AGN SEDs, in particular the mid-IR spectral index, can be used to
constrain the radial dust cloud distribution power-law index 'a', while other
parameters are more difficult to assess using SEDs only. Interferometry adds
important additional information for modeling when interpreted simultaneously
with the SED. Although type 2 AGN can, in principle, be used to constrain model
parameters as well, obscuration effects make the analysis more ambiguous. We
propose a simple, interferometry-based method to distinguish between "compact''
and "extended'' radial dust distributions without detailed modeling of the data
and introduce a way to easily determine individual or sample average model
parameters using the observed optical depth in the silicate feature and the
mid-IR spectral index.
