New VLA Observations of NH 3 in S140

Abstract

The S140 molecular cloud was observed in the NH<SUB>3</SUB> (1, 1) and (2, 2) lines with 5" resolution. Compared with the previous VLA observations, the new observations have 3 times better flux sensitivity, 4 times better spatial resolution, and 2.5 times better velocity resolution. These advantages allowed the detection of 80%-85% of the single-dish flux in the two NH<SUB>3</SUB> lines. The NH<SUB>3</SUB>emission region consists of a long filament perpendicular to the optical bright rim and an arclike structure along the edge of the bright rim. Within 15" of IRS 1, there is an absence of NH<SUB>3</SUB>emission which is probably caused by a true decrease in NH<SUB>3</SUB> column density, not by missing short spacings or changes in the partition function due to a temperature increase. Comparison with a multitransition analysis of CS observations shows that this low NH<SUB>3</SUB> column density indicates a low NH<SUB>3</SUB> abundance in the dense gas near the infrared sources rather than an absence of molecular gas. The gas temperature is derived from the NH<SUB>3</SUB> data and can be accounted for mostly by heating from IRS 1-IRS 3. We also detected a compact continuum source at 2.7 mm with the Owens Valley Millimeter Interferometer. This continuum source coincides with the peak of low-J CS emission and an NH<SUB>3</SUB> emission peak. The NH<SUB>3</SUB> lines at this position are unusually wide, and the profiles are consistent with models of gravitational collapse.