Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Properties of the circumnuclear medium in Active Galactic Nuclei   We propose a classification scheme for the circumnuclear medium of AGNs based
on their location in the A_V - N_H plane (related to dust absorption and gas
absorption, respectively). We present evidence that the A_V/N_H ratio is often
lower than the Galactic value. This is shown by the broad line ratios of a
sample of intermediate Seyferts, and by the optical/X-ray ratio of line
selected (as opposed to color selected) AGNs. We point out the implications for
the physical properties of the absorber. A complete classification would
require a third axis, related to the density of the absorber and/or its
distance from the AGN.

18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat