ANATOMY OF THE GEMINI OB1 MOLECULAR CLOUD COMPLEX

We have investigated the large-scale morphology and properties of the molecular gas in the Gem OB1 cloud complex by mapping over 32 deg(2) ( 177 pc x 221 pc) of the complex in (CO)-C-12(J = 1-0) and (CO)-C-13(J = 1-0) at 50 '' sampling with QUARRY on the FCRAO 14 m telescope. The most striking characteristic of the molecular line images are the seri es of arc- and ring-shaped structures found on spatial scales from a f ew parsecs in diameter up to at least 35 pc. The morphology and in som e instances the kinematics suggest that these features represent swept -up molecular material, most likely from expanding H II regions and wi nd blown bubbles. The kinetic temperatures and column densities of the molecular gas were derived from the (CO)-C-12 and (CO)-C-13 data usin g the LTE analysis. Most of the molecular gas was found to have kineti c temperatures of less than or similar to 10 K, and 50% of the mass of gas is contained in lines of sight with H-2 column densities less tha n or similar to 2 x 10(21) cm(-2). It was found that only 10% of the m olecular mass is contained in lines of sight with column densities in excess of 10(22) cm(-2), and that these regions are found almost exclu sively near the massive star forming regions within the arcs and rings of molecular gas. The average H-2 densities in areas with (CO)-C-13 e mission are between 65-120 cm(-3), consistent with previous studies of cloud complexes, and is independent of whether the regions contains m assive star formation or not. For the Gem OB1 complex as a whole, the average H-2 density is 1.2 cm(-3), which is only a few times the avera ge atomic hydrogen density in the interstellar medium. We suggest an o verall picture for the Gem OB1 complex in which most of the molecular gas is contained in relatively cold, low column density molecular mate rial. The high column density regions in the Gem OB1 complex form thro ugh the external compression of the molecular gas by the winds and H I I regions from newly formed massive stars. Thus once massive star form ation is initiated, the structure and further evolution of the cloud c omplex is largely a result of the interactions of expanding H II regio ns and stellar winds with the ambient molecular material.