Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: H2O megamasers: Accretion disks, jet interaction, outflows or massive
  star formation?   The 25 years following the serendipitous discovery of megamasers have seen
tremendous progress in the study of luminous extragalactic H$_2$O emission.
Single-dish monitoring and high resolution interferometry have been used to
identify sites of massive star formation, to study the interaction of nuclear
jets with dense molecular gas and to investigate the circumnuclear environment
of active galactic nuclei (AGN). Accretion disks with radii of 0.1--3 pc were
mapped and masses of nuclear engines of order 10$^{6}$--10$^{8}$ M$_{\odot}$
were determined. So far, $\sim$50 extragalactic H$_2$O maser sources have been
detected, but few have been studied in detail.

9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn