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Non-equilibrium excitation of methanol in Galactic molecular clouds: multi-transitional observations at 2 mm

V. I. Slysh·S. V. Kalenskii·I. E. Val'tts·V. V. Golubev·K. Mead
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Abstract

We observed 14 methanol transitions near lambda=2 mm in Galactic star-forming regions. Broad, quasi-thermal J(0)-J(-1)E methanol lines near 157 GHz were detected toward 73 sources. Together with the 6(-1)-5(0)E and 5(-2)-6(-1)E lines at 133 GHz and the 7(1)-7(0)E line at 165 GHz, they were used to study the methanol excitation. In the majority of the observed objects, the Class I 6(-1)-5(0)E transition is inverted, and the Class II 5(-2)-6(-1)E and 6(0)-6(-1)E transitions are overcooled. This is exactly as predicted by models of low gain Class I masers. The absence of the inversion of Class II transitions 5(-2)-6(-1)E and 6(0)-6(-1)E means that quasi-thermal methanol emission in all objects arises in areas without a strong radiation field, which is required for the inversion.

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V. I. Slysh, S. V. Kalenskii, I. E. Val'tts, V. V. Golubev, K. Mead. 1999-06-04. Non-equilibrium excitation of methanol in Galactic molecular clouds: multi-transitional observations at 2 mm. https://doi.org/10.1086/313240

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