A recent high angular resolution extinction map toward the most opaquemolecular globule, Globule 2, in the Coalsack Nebula revealed that it containsa strong central ring of dust column density. This ring represents a region ofhigh density and pressure that is likely a transient and possibly turbulentstructure. Dynamical models suggest that the ring has formed as a result of asudden increase in external pressure which is driving a compression wave intothe Globule. Here we combine the extinction measurements with a detailed studyof the C18O (1-0) molecular line profiles toward Globule 2 in order toinvestigate the overall kinematics and, in doing so, test this dynamical model.We find that the ring corresponds to an enhancement in the C18O non-thermalvelocity dispersion and non-thermal pressure. We observe a velocity gradientacross the Globule that appears to trace two distinct systematic subsonicvelocity flows that happen to converge within the ring. We suggest, therefore,that the ring has formed as two subsonic flows of turbulent gas merge withinthe Globule. The fact that the outer layers of the Globule appear stableagainst collapse yet there is no centrally condensed core, suggests that theGlobule may be evolving from the outside in and has yet to stabilize,confirming its youth.
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