VLA observations of 43-GHz continuum and CS J= 1-0 emission from Orion-IRc2 and the hot core

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Abstract
We have used the VLA to image at 2-arcsec resolution the Orion-IRc2 region in 43-GHz continuum and CS(1-0) emission. In the continuum, radio sources I and B are detected together with an extended emission component which peaks at source I. Comparison of this extended component with lower frequency data suggests that it is free-free emission from a dusty H ii region ionized by source I. The compact CS(1-0) emission originates from the hot core, the compact ridge and the western clump. The hot core component has a line brightness temperature of ∼ 150 K, and is optically thick. We derive an abundance for the CS relative to H2 in the hot core of 1.2 × 10−8, considerably higher than the previous upper limit based on a single-dish spectral line survey. The difference can be explained as being due to beam dilution of the hot core component in the earlier, low-resolution study, and the confusion of the hot core with emission from the extended ridge. A similar result is also suggested for the sulphur-bearing molecules SO and SO2, and existing models of sulphur chemistry are unable to reproduce these new abundance estimates. We conclude that models extending to higher temperatures and densities are required to explain these data.

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