Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: IR emission from AGNs   Unified schemes of active galactic nuclei (AGN) require an obscuring dusty
torus around the central source, giving rise to type 1 line spectrum for
pole-on viewing and type 2 characteristics in edge-on sources. Infrared
radiation at its different wavelengths is the best probe of the dust
distribution, whether the torus orientation is edge-on or pole-on. The observed
IR is in broad agreement with the unified scheme but serious problems remained
in all early modeling efforts. In spite of a general awareness that the dust
must be concentrated in clouds, clumpiness remained the one major ingredient
missing in those radiative transfer studies because of the inherent
difficulties it presents. We have recently developed the formalism to handle
dust clumpiness and our results indicate that its inclusion may resolve the
difficulties encountered by the previous theoretical efforts. We show that
these problems find a natural explanation if the dust is contained in \about\
5--10 clouds along radial rays through the torus. The spectral energy
distributions (SED) of both type 1 and type 2 sources are properly reproduced
from different viewpoints of the same object if the optical depth of each cloud
is \ga 40 at visual wavelengths and the clouds' mean free path increases
roughly in proportion to radial distance.

16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg