CO–0.30–0.07: A PECULIAR MOLECULAR CLUMP WITH AN EXTREMELY BROAD VELOCITY WIDTH IN THE CENTRAL MOLECULAR ZONE OF THE MILKY WAY

摘要

The high?velocity dispersion compact cloud CO–0.30–0.07 is a peculiar molecular clump discovered in the central molecular zone of the Milky Way, which is characterized by its extremely broad velocity emissions () despite the absence of internal energy sources. We present new interferometric maps of the cloud in multiple molecular lines in frequency ranges of 265–269 GHz and 276–280 GHz obtained using the Submillimeter Array, along with the single-dish images previously obtained with the ASTE 10 m telescope. The data show that the characteristic broad velocity emissions are predominantly confined in two parallel ridges running through the cloud center. The central ridges are tightly anticorrelated with each other in both space and velocity, thereby sharply dividing the entire cloud into two distinct velocity components (+15 and +55 km s?1). This morphology is consistent with a model in which the two velocity components collide with a relative velocity of 40 at the interface defined by the central ridges, although an alternative explanation with a highly inclined expanding-ring model is yet to be fully invalidated. We have also unexpectedly detected several compact clumps ( pc in radius) likely formed by shock compression. The clumps have several features in common with typical star-forming clouds: high densities (), rich abundances of hot-core-type molecular species, and relatively narrow velocity widths apparently decoupled from the furious turbulence dominating the cloud. The cloud CO–0.30–0.07 is possibly at an early phase of star formation activity triggered by the shock impact.