Measurements of the J=2-1 Lines of CS and C¹⁸O toward the Star-forming Region W49A North

Observations of the W49A North star-forming region in the J = 2-1 line of CS have been made with the BIMA array with an angular resolution of 46 × 38; complementary observations in the J = 2-1 line of C¹⁸O and J = 3-2 line of C³⁴S were made with the IRAM 30 m telescope, with angular resolutions of 12'' and 17'' respectively. The molecular complex is elongated along a diagonal from northeast to southwest. The position-velocity diagrams for CS convolved to 12'' resemble those of C¹⁸O and the J = 5-4 line of C³⁴S (from Serabyn et al.). There is a change in velocity along the major axis of the molecular complex. Most spectra toward W49A North show two main velocity components, the relative intensities of which vary with position along the major axis of the molecular complex. At the higher resolution of ~4'', absorption of the continuum emission at 3 mm by CS is clearly observed. The apparent velocity gradient is seen to be part of a C-shaped distribution in the CS position-velocity image. Furthermore, as is found in the J = 1-0 HCO⁺ data by Welch et al., the optically thick CS J = 2-1 line exhibits an inverse P Cygni profile toward H II region G. These two characteristics of the CS data lend support to the global collapse model (Welch et al.). The high-resolution CS profiles in the central region all show varying degrees of absorption. At lower resolution the surrounding CS emission fills in much of the absorption and the inverse P Cygni shape disappears.