Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gas Dynamics in Central Parts of Galaxies   Asymmetries in galactic potentials, either self-induced, or caused by a
passing companion, play an important role in global gas dynamics in galaxies.
In particular, they are able to trigger gas inflow, which in turn feeds nuclear
activity. In the inner kiloparsec, the inflowing gas becomes subject to various
resonances induced by asymmetry in the potential. This produces complicated gas
morphology and dynamics seen in the nuclear rings and spirals. Formation of
nuclear rings is related to barred galaxies, and explained by the orbital
structure in bars. One can get basic understanding of weak nuclear spirals from
the linear wave theory, but stronger spirals are likely to be out of the linear
regime, and they appear as spiral shocks in hydrodynamical models. In addition,
nuclear stellar bars are observed in a considerable fraction of disc galaxies,
often nested inside the large bar; their orbital structure further modifies the
nuclear gas dynamics. If a massive black hole (MBH) is present in the galactic
centre, it governs the resonances even beyond its classically defined sphere of
influence. Since resonances shape gas dynamics in the nuclear region, the
central black hole should be able to regulate gas flow around itself.

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The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom