A Large-Scale 13CO Mapping of the W 49 A Molecular Cloud Complex

Abstract

Abstract We present $^{13}$CO ($J$$=$ 1-0) and C$^{18}$O ($J$$=$ 1-0) maps of the W 49 A molecular cloud complex observed at a resolution of 17$''$ (HPBW). Fourteen features (MHH-1 to MHH-14) were identified in the $^{13}$CO velocity channel maps, most of them distributed within an area of 6$'$ (20 pc) in diameter with their total mass amounting to 1.7 $\times$ 10$^{6}M_\odot$. The features have a three-dimensional velocity dispersion of 8 km s$^{-1}$, which leads to a mean free time per feature of 10$^{6}$yr. This suggests that they are interacting one another in a region of $\sim$20 pc in diameter. The feature MHH-1, which corresponds to W 49 N, is unique in that it exhibits a large velocity width (15 km s$^{-1}$ FWHM) and is compact in size (2.3 pc $\times$ 3.0 pc FWHM), while containing a large mass of 2.4 $\times$ 10$^{5}M_\odot$. This indicates that the free-fall time of MHH-1 is on the order of 10$^{5}$yr, an order of magnitude smaller than that of the entire complex. It has turned out that MHH-1 has a smaller spatial width at $V_{\rm LSR}$$\lesssim$ 8 km s$^{-1}$ than at $\gtrsim$8 km s$^{-1}$. This result, together with the line-profile characteristics of various optically thin lines, suggests that at least two massive clouds with different radial velocities exist toward MHH-1. The massive compact feature may have been produced by the interaction of the two different velocity clouds.