6-CENTIMETER FORMALDEHYDE ABSORPTION TOWARD THE SAGITTARIUS-B STAR-FORMING COMPLEX

Observations of the 6 cm transition of H2CO (formaldehyde) toward the Sgr B massive star-forming complex have been carried out using the VLA . The purpose of this 15'' resolution absorption study was to determin e the parameters ( e.g., velocities, optical depths, and line widths) of the molecular clouds that lie along the line of sight. The H2CO clo uds studied have velocities in the range -130 km s(-1) < upsilon(LSR) < +130 km s(-1). The H2CO spectrum of Sgr B1 is very different from th at of Sgr B2. The optical depths of the molecular clouds associated wi th Sgr B2 are greater than 1, while the opacities are less than 1 for the molecular clouds associated with Sgr B1. Thus, much of the molecul ar material in Sgr B1 seems to have dispersed, suggesting that Sgr B1 is more evolved than Sgr B2. This same conclusion was reached by Mehri nger et al. on the basis of radio continuum observations. In Sgr B2, H 2CO spectra vary dramatically from one position to another, which sugg ests that the H II regions lie at different depths within the clouds. Thus, several isolated events may have triggered star formation throug hout Sgr B2, in contrast to many current models which suggest a single global event is responsible. The properties of a number of clouds whi ch are in the central part of the Galaxy, but are not associated with the H II regions, are briefly discussed.