A submillimetre continuum study of S 140/L 1204: the detection of three new submillimetre sources and a self-consistent model for the region

We present submillimetre continuum observations of the L 1204/S 140 complex in broad bands centred at 450, 800 and 1100μm. The morphology of the region is similar at all three wavelengths, with the emitting region compact, about 90 arcsec in diameter, and centrally peaked around the cloud core. Three new submillimetre continuum sources are observed which are not coincident with any previously known near or mid-infrared sources. We designate the sources S 140-SMM1-3. SMM1 is roughly coincident with a previously known NH3 clump and 2.7mm source, and near-IR reflection nebulosity from the surface of SMM2 has previously been seen. The three submillimetre continuum sources may be protostellar in nature, although it is not possible to determine whether they are gravitationally bound, since virial mass estimates are disrupted by the presence of an energetic bipolar outflow. For this reason, earlier claims that the 2.7mm source in SMM1 is collapsing appear somewhat premature. The observation that SMM1 and SMM2 lie either side of the infrared sources, in a line roughly perpendicular to the direction of the bipolar outflow, imply they may be the remnants of a large-scale disk. Comparison of the continuum emission with previous high resolution CS, NH3 and CI observations provides evidence that, for the first time, demonstrates the photon-dominated region and outflow are intimately linked. The only scenario that is able to explain all of the available molecular and atomic emission line data and our submillimetre continuum data, is one in which the outflow has expanded towards the edge of the molecular cloud and the edge of the blueshifted outflow lobe is now bounded by the expanding HII region. The NH3 and continuum emission emanate from the inner edge of the outflow lobe, shielded from the external UV field. A plot of the 800μm flux against N(C18O) implies that the dust/gas mass ratio is close to the canonical value (~1%) at the lower end of the observed extinction range (Av≤70), but for the highest observed extinctions (Av=70-100) the continuum flux density increases rapidly, implying a higher dust/gas mass ratio is appropriate (~2-5%), possibly indicating freeze-out of gas onto dust grains