Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dust in the central parsecs of unobscured AGN: more challenges to the
  torus   A parsec-scale dusty torus is thought to be the cause of Active Galactic
Nuclei (AGN) dichotomy in the 1/2 types, narrow/broad emission lines. In a
previous work, on the basis of parsec-scale resolution infrared / optical dust
maps it was found that dust filaments, few parsecs wide, several hundred
parsecs long, were ubiquitous features crossing the centre of type 2 AGN, their
optical thickness being sufficient to fully obscure the optical nucleus. This
work presents the complementary view for type 1 and intermediate-type AGN. The
same type of narrow, collimated, dust filaments are equally found at the centre
of these AGN. The difference now resides in their location with respect to the
nucleus, next to it but not crossing it, as it is the case in type 2, and their
reduced optical thickness towards the centre, $A_V \lesssim 1.5 \rm{mag}$,
insufficient to obscure at UV nucleus wavelengths. It is concluded that large
scale, hundred pc to kpc long, dust filaments and lanes, reminiscent of those
seen in the Milky Way, are a common ingredient to the central parsec of
galaxies. Their optical thickness changes along their structure, in type 2
reaching optical depths high enough to obscure the nucleus in full. Their
location with respect to the nucleus and increasing gradient in optical depth
towards the centre could naturally lead to the canonical type 1/2 AGN
classification, making these filaments to play the role of the torus. Dust
filaments and lanes show equivalent morphologies in molecular gas. Available
gas kinematic indicates mass inflows at rates $ < ~ 1 M\odot~ yr^{-1}$.

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The categories of this paper are: gr-qc
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: physics
19
The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: hep-ph
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The categories of this paper are: nlin