The internal structure of molecular clouds. I. C1C180 , C34S and NH3 maps of the DR 21/W 75S region.

Maps of a ∼8' × 17' area around DR21/W75S with resolutions of 10" to 40" in the (J,K) = (1,1), (2,2), (3,3) and (4,4) inversion lines of ammonia, the J = 2-1 line of C¹⁸O and the J = 3-2 line of C³⁴S are presented. The molecular emission arises in a column-like region, which is elongated N-S, with a major-to-minor axis ratio of >6-to-1. The total mass of the region with V_LSR -3 km s^-1, is 3 10⁴ M_sun, and the region with V_LSR +9 km s^-1 is 1.5 10³ M_sun. In addition to the compact HII region DR 21 and the OH/H₂O/methanol maser source DR 21(OH)/W75S, we find 11 additional maxima. The C¹⁸O spectra show line wings for DR 21, W 75S and NH₃4, indicating the presence of outflow sources. Toward DR 21, low intensity C¹⁸O emission follows the direction of the outflow seen in vibrationally excited H₂. From our C¹⁸O data, we estimate that the mass involved in the western lobe of this outflow is 1.8 10³ M_sun, and the energy is 7 10⁴⁶ ergs. The velocity shift and overall extent of the eastern lobe is less definite. There must be other, weaker outflow sources, since the emission from the whole region shows a large amount of tangled filamentary structure. More extended, apparently smooth molecular emission probably consists of a large number of dense, compact sources. Averaged over 40", the molecular cores near DR 21 and W 75 S have kinetic temperatures, T_kin > 35K and H₂ densities > 105 cm^-3. In more extended regions, T_kin ∼ 20K. The linewidths are > 5 times the thermal width. The detection of weak C³⁴S, J = 3 - 2 line emission in the envelope indicates that the NH₃ emission is thermalized. The low intensity of the optically thick NH₃ emission indicates a large number of clumps, each smaller than the beam. The (NH₃/C¹⁸O) ratio in the envelope is comparable to the ratio normally found for dust clouds. A comparison with dust continuum measurements indicates no significant difference between the (NH₃/H₂) ratio in the extended and compact regions.

The combination of absorption in the (J,K)=(1,1) and (2,2) lines, and emission in the (3,3) line, found toward DR 21, does not necessarily require maser emission, but might be explained by the presence of two clouds with kinetic temperatures ∼65 K and 22 K. The warmer cloud is located 20" south of the HII region.