AAS 207th Meeting, 8-12 January 2006
Session 81 ISM: From Dark to Blinded
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[81.06] Anomalous H2CO Absorption in the L1204/S140 Region and a Comparison with CO(1-0) Emission

M.I. Rodriguez (STScI), L. Loinard (CRyA), R. J. Allen (STScI), V. Escalante (CRyA), T. Wiklind (STScI)

We report observations of the region including the S140 H\alpha arc and the molecular/dust cloud L1204 with the Onsala 25-m telescope in the 6 cm (111-110) transition of H2CO. This spectral line is seen here in absorption against the cosmic microwave background, and is a tracer for the presence of relatively cold molecular gas of intermediate density. We have detected H2CO absorption in 16 pointing positions. We compare our results to earlier maps of the region in the CO(1-0) line. In general the distributions of H2CO and CO are similar, but there are some notable differences including the fact that the maximum H2CO absorption is clearly separated by a full 10' (~ 3 pc) from the CO peak. This CO peak is nearly coincident with the H\alpha arc S140, and from a consideration of a different sensitivities of H2CO and CO to local excitation conditions. We conclude that the CO emission in this region is bright because of local heating. The H2CO 6-cm line apparently traces the bulk of the molecular gas, which is located behind S140. The H2CO spectra show a complex velocity structure of at least two main parts to the L1204 molecular cloud.

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