DENSE GAS IN THE DR-21 REGION - HIGH-RESOLUTION IMAGING OF THE NH3 INVERSION LINES

Three arcsecond angular resolution images of the (J, K) = (1, 1) and ( 3, 3) inversion lines of NH3 toward the DR 21 H II region are presente d. There is absorption in the (1, 1) line toward DR 21 and emission to the northwest, northeast, southwest, and south. The NH3 region found in emission in the (1, 1) line southwest of DR 21 is likely the same c loud seen in absorption toward the H II region. If the emission and ab sorption regions are taken as one cloud, this is the most massive and largest near DR 21. In the (J, K) = (1, 1) line this cloud shows a vel ocity gradient of 15 km s(-1) pc(-1). To the northeast, low-brightness continuum emission extends over a larger region, and there is little NH3. In the (1, 1) emission line, filament-like NH3 emission regions a re elongated N-S > 20 ''; for most, the emission is almost unresolved in the E-W direction. In most cases these filaments have a position an gle that is very close to that measured for the molecular cloud over > 10'. The NH3 emission line delineates the location of the denser mole cular gas. The presence of dense clouds south and southwest of the con tinuum source and the sharp falloff of the H II continuum intensity to the southwest gives support to the notion that the expansion of the H II region is halted by dense neutral gas to the southwest. The struct ures traced by the (3, 3) transition differ greatly from those found f or the (1, 1) line. Toward the H II region DR 21, there are several (3 , 3) emission maxima, two of which exhibit prominent negative velocity line wings. The (3, 3) line traces the hotter shocked gas. Given the negative velocity wings, the morphology of the (3, 3) line emission an d the location of the NH3 emission relative to the powerful outflow se en in vibrationally excited H-2 and other molecules, we conclude that the NH3 represents the remnant material that has survived the powerful outflow. We estimate the location of the outflow source assuming that this is located near the shocked gas midway between the two NH3 (3,3) maxima with prominent negative velocity line wings.