Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ionized nebulae surrounding brightest cluster galaxies   We present IFU observations of six emission-line nebulae that surround the
central galaxy of cool core clusters. Qualitatively similar nebulae are
observed in cool core clusters even when the dynamics and possibly formation
and excitation source are different. Evidence for a nearby secondary galaxy
disturbing a nebula, as well as AGN and starburst driven outflows are presented
as possible formation mechanisms. One nebula has a rotation velocity of the
same amplitude as the underlying molecular reservoir, which implies that the
excitation or formation of a nebula does not require any disturbance of the
molecular reservoir within the central galaxy. Bulk flows and velocity shears
of a few hundred km/s are seen across all nebulae. The majority lack any
ordered rotation, their configurations are not stable so the nebulae must be
constantly reshaping, dispersing and reforming. The dimmer nebulae are
co-spatial with dust features whilst the more luminous are not. Significant
variation in the ionization state of the gas is seen in all nebulae through the
non-uniform [NII]/H_alpha ratio. There is no correlation between the line ratio
and H_alpha surface brightness, but regions with excess blue or UV light have
lower line ratios. This implies that UV from massive, young stars act in
combination with an underlying heating source that produces the observed
low-ionization spectra.

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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys