G345.45+1.50 ^13^CO(3-2) clumps

The ^13^CO(3-2) line was mapped toward the whole ring using the Atacama Pathfinder Experiment (APEX) telescope. The observations cover 17'x20' in the sky with a spatial resolution of 0.2pc and an rms of ~1K at a spectral resolution of 0.1km/s. The ring is found to be expanding with a velocity of 1.0km/s, containing a total mass of 6.9x10^3^M_{sun}_, which agrees well with that determined using 1.2mm dust continuum emission.

An expansion timescale of ~3x10^6^yr and a total energy of ~7x10^46^erg are estimated. The origin of the ring might have been a supernova explosion, since a 35.5cm source, J165920-400424, is located at the center of the ring without an infrared counterpart. The ring is fragmented, and 104 clumps were identified with diameters of between 0.3 and 1.6pc, masses of between 2.3 and 7.5x10^2^M_{sun}_, and densities of between ~10^2^ and ~10^4^cm^-3^.

At least 18% of the clumps are forming stars, as is shown in infrared images. Assuming that the clumps can be modeled as Bonnor-Ebert spheres, 13 clumps are collapsing, and the rest of them are in hydrostatic equilibrium with an external pressure with a median value of 4x10^4^K/cm^3^. In the region, the molecular outflow IRAS 16562-3959 is identified, with a velocity range of 38.4km/s, total mass of 13M_{sun}_, and kinematic energy of 7x10^45^erg.

Finally, five filamentary structures were found at the edge of the ring with an average size of 3pc, a width of 0.6pc, a mass of 2x10^2^M_{sun}_, and a column density of 6x10^21^cm^-2^.