Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Ionization of the Emission Line Gas in Nearby Powerful Radio
  Galaxies   In this article I review the dominant physical mechanisms in the extended
emission line regions (EELR) of powerful radio galaxies at low redshifts and,
in particular, the balance between jet-induced shocks and AGN photoionization.
I consider the evidence for jet-induced shocks based on morphological,
kinematical and ionization (diagnostic diagram) information. Although each of
these three types of information separately provides some evidence for the
effects of jet-induced shocks, this evidence is often ambiguous. The major
advance in recent years has been to combine morphological, kinematical and
diagnostic diagram approaches. In this way it has been possible to show that
jet-induced shocks dominate the ionization and acceleration of the EELR along
the radio axes of many powerful radio galaxies. However, AGN photoionization is
likely to remain the dominant mechanism in the nuclear regions of radio
galaxies in which the radio sources extend well beyond the emission line
regions.

15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ