Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ground-state OH observations towards NGC 6334   We have made observations of the four hyperfine transitions of the 2Pi(3/2),
J=3/2 ground state of OH at 1612, 1665, 1667 and 1720 MHz and the related
1.6-GHz continuum emission, towards NGC 6334 using the Australia Telescope
Compact Array. The observations covered all the major radio continuum
concentrations aligned along the axis of NGC 6334 (V, A to F). We have detected
seven OH masers plus a possible faint eighth maser; two of these masers are
located towards NGC 6334-A. Absorption at 1665 and 1667 MHz was detected
towards almost all the continuum distribution. All transitions showed non-LTE
behaviour. The 1667-/1665-MHz intensity ratios ranged from 1.0 to 1.2,
significantly less than their LTE value of 1.8. The results of the OH `Sum
Rule' suggest that this discrepancy cannot be explained solely by high optical
depths. The 1612- and 1720-MHz line-profiles showed conjugate behaviour whereby
one line was in absorption and the other in emission. In addition, the profiles
commonly showed a flip from absorption to emission and vice versa, which has
been interpreted as a density gradient. The OH line-to-continuum distribution,
optical depth and velocity trends are consistent with a bar-like shape for the
molecular gas which wraps around the continuum emission.

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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
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The categories of this paper are: cs