Collisional Excitation of SO2 in Cold Molecular Clouds
Department of Astrophysics. CAB. INTA-CSIC. Crta TorrejOn km 4.28850 Torrejon de Ardoz., Madrid, Spain
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Using recently calculated collisional rates for SO2 with ortho and para molecular hydrogen, we have calculated the expected emission of the centimeter wavelength lines of SO2 for the physical conditions previling in dark molecular clouds. We have found that the transition connecting the metastable 202 level with the 111 one will be in absorption against the cosmic background for a large range of densities. The 404-313 line is found to be masering for densities below a few 104 cm−3. We have observed the 111-202 transition with the GBT telescope towards some dark clouds. The line is observed, as expected, in absorption and provides an abundance of SO2 in these objects of a few 10−10. The potential use of millimeter lines of SO2 as tracers of the physical conditions of dark clouds is discussed.
© Owned by the authors, published by EDP Sciences, 2012