Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An analysis of HCN observations of the Circumnuclear Disk at the
  galactic centre   The Circumnuclear Disk (CND) is a torus of dust and molecular gas rotating
about the galactic centre and extending from approximately 1.6pc to 7pc from
the central massive black hole, SgrA*. Large Velocity Gradient modelling of the
intensities of the HCN 1-0, 3-2 and 4-3 transitions is used to infer hydrogen
density and HCN optical depth. From HCN observations we find the molecular
hydrogen density ranges from 0.1 to 2 $\times$ 10$^{6}$ cm$^{-3}$, about an
order of magnitude less than inferred previously. The 1-0 line is weakly
inverted with line-centre optical depth approx $-$0.1, in stark contrast to
earlier estimates of 4. The estimated mass of the ring is approximately 3 $-$ 4
$\times$ 10$^{5}$M$_{\odot}$ consistent with estimates based on thermal dust
emission. The tidal shear in the disk implies that star formation is not
expected to occur without some significant triggering event.

34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
2
The categories of this paper are: math