Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A direct image of the obscuring disk surrounding an active galactic
  nucleus   Active galactic nuclei (AGN) are generally accepted to be powered by the
release of gravitational energy in a compact accretion disk surrounding a
massive black hole. Such disks are also necessary to collimate powerful radio
jets seen in some AGN. The unifying classification schemes for AGN further
propose that differences in their appearance can be attributed to the opacity
of the accreting material, which may obstruct our view of the central region of
some systems. The popular model for the obscuring medium is a parsec-scale disk
of dense molecular gas, although evidence for such disks has been mostly
indirect, as their angular size is much smaller than the resolution of
conventional telescopes. Here we report the first direct images of a pc-scale
disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured
AGN. The disk is viewed nearly edge-on, and individual clouds within the
ionised disk are opaque to high-energy radiation, consistent with the unifying
classification scheme. In projection, the disk and AGN axes align, from which
we infer that the ionised gas disk traces the outer regions of the long-sought
inner accretion disk.

11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio