G345.45+1.50: An expanding ring-like structure with massive star formation
Journal article, 2016

Context. Ring-like structures in the interstellar medium (ISM) are commonly associated with high-mass stars. Kinematic studies of large structures in giant molecular clouds (GMCs) toward these ring-like structures may help us to understand how massive stars form. Aims. The origin and properties of the ring-like structure G345.45+1.50 is investigated through observations of the 13CO(3-2) line. The aim of the observations is to determine the kinematics in the region and to compare physical characteristics estimated from gas emission with those previously determined using dust continuum emission. This area in the sky is well suited for studies like this because the ring is located 1°5 above the Galactic plane at 1.8 kpc from the Sun, thus molecular structures are rarely superposed on our line of sight, which minimizes confusion effects that might hinder identifying of individual molecular condensations. Methods. The 13CO(3-2) line was mapped toward the whole ring using the Atacama Pathfinder Experiment (APEX) telescope. The observations cover 17? × 20? in the sky with a spatial resolution of 0.2 pc and an rms of ~1 K at a spectral resolution of 0.1 km s-1. Results. The ring is found to be expanding with a velocity of 1.0 km s-1, containing a total mass of 6.9 × 103M?, which agrees well with that determined using 1.2 mm dust continuum emission. An expansion timescale of ~3 × 106 yr and a total energy of ~7 × 1046 erg are estimated. The origin of the ring might have been a supernova explosion, since a 35.5 cm 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 1.6 pc, masses of between 2.3 and 7.5 × 102M?, and densities of between ~102 and ~ 104 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 4 × 104 K cm-3. In the region, the molecular outflow IRAS 16562-3959 is identified, with a velocity range of 38.4 km s-1, total mass of 13 M?, and kinematic energy of 7 × 1045 erg. Finally, five filamentary structures were found at the edge of the ring with an average size of 3 pc, a width of 0.6 pc, a mass of 2 × 102M?, and a column density of 6 × 1021 cm-2.

ISM: clouds

ISM: molecules

ISM: kinematics and dynamics


Stars: massive


Stars: formation


Cristian López-Calderón

University of Chile (UCH)

Atacama Large Millimeter-submillimeter Array (ALMA)

National Radio Astronomy Observatory

Leonardo Bronfman

University of Chile (UCH)

L.-Å. Nyman

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

G. Garay

University of Chile (UCH)

I. de Gregorio-Monsalvo

European Southern Observatory Santiago

European Southern Observatory (ESO)

Atacama Large Millimeter-submillimeter Array (ALMA)

Per Bergman

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 595 Art no A88- A88

Subject Categories

Astronomy, Astrophysics and Cosmology


Onsala Space Observatory



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