Infall through the evolution of high-mass star-forming clumps
2016
With the GREAT receiver at the
Stratospheric Observatoryfor
Infrared Astronomy(SOFIA), nine massive molecular clumps have been observed in the ammonia 32+−22− line at 1.8 THz in a search for signatures of
infall. The sources were selected from the ATLASGAL submillimeter dust continuum survey of our Galaxy. Clumps with high masses covering a range of evolutionary stages based on their infrared properties were chosen. The ammonia line was detected in all sources, leading to five new detections and one confirmation of a previous detection of redshifted absorption in front of their strong THz continuum as a probe of
infallin the clumps. These detections include two clumps embedded in
infrared dark clouds. The measured velocity shifts of the absorptions compared to optically thin C 17 O (3–2) emission are 0.3–2.8 km s −1 , corresponding to fractions of 3% to 30% of the
free-fallvelocities of the clumps. The ammonia
infallsignature is compared with complementary data of different transitions of HCN, HNC, CS, and HCO + , which are often used to probe
infallbecause of their blue-
skewed lineprofiles. The best agreement with the ammonia results is found for the HCO + (4–3) transitions, but the latter is still strongly blended with emission from associated outflows. This outflow signature is far less prominent in the THz ammonia lines, which confirms it as a powerful probe of
infallin molecular clumps.
Infallrates in the range from 0.3 to 16 × 10 −3 M� /yr were derived with a tentative correlation with the virial parameters of the clumps. The new observations show that
infallon clump scales is ubiquitous through a wide range of evolutionary stages, from L/M covering about ten to several hundreds.
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