Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multiwavelength WHAM Observations of Extra-planar Warm Ionized Gas in
  the Galaxy   We report on observations of several optical emission lines toward a variety
of newly revealed faint, large-scale H-alpha-emitting structures in the warm
ionized medium (WIM) of the Galaxy. The lines include [N II] 6583, [N II] 5755,
[S II] 6716, [O III] 5007, and He I 5876 and were obtained with the Wisconsin
H-Alpha Mapper (WHAM) toward sightlines that probe both large filamentary
features and the more diffuse WIM, from the outer Perseus spiral arm to the
inner Galaxy. These emission lines allow us to explore the temperature and
ionization conditions within the emitting gas and their variations between the
different emission regions. We compare the relative intensities of the emission
lines toward these faint H II structures to brighter, classical O star H II
regions. We find that the line ratios of [N II]/H-alpha and [S II]/H-alpha are
generally high, while [O III]/H-alpha and He I/H-alpha are generally low in the
diffuse WIM and in the faint filamentary structures. This suggests that the gas
is warmer, in a lower ionization state, and ionized by a softer spectrum than
the gas in classical H II regions surrounding O stars, the presumed ionization
source for the WIM. In addition, we find differences in the physical conditions
between the large filamentary structures and the more diffuse WIM, suggesting
that the filaments are regions of higher density, not geometrical projections
of folds in large sheet-like or shell-like structures.

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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
4
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: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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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: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex