Ground-state OH observations towards NGC 6334

Abstract

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.

arXiv comment12 pages, 12 figures, accepted for publication in MNRAS

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• Continuum emission associated with 6.7-GHz methanol masers
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