Infall through the evolution of high-mass star-forming clumps^⋆

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: wyrowski@mpifr-bonn.mpg.de; rguesten@mpifr-bonn.mpg.de; kmenten@mpifr-bonn.mpg.de; hwiese@mpifr-bonn.mpg.de; csengeri@mpifr-bonn.mpg.de; heyminck@mpifr-bonn.mpg.de; bklein@mpifr-bonn.mpg.de; bklein@mpifr-bonn.mpg.de; ckoenig@mpifr-bonn.mpg.de; jurquhart@mpifr-bonn.mpg.de
² University of Applied Sciences Bonn-Rhein-Sieg, Grantham-Allee 20, 53757 Sankt Augustin, Germany

Received: 20 April 2015
Accepted: 5 October 2015

Abstract

With the GREAT receiver at the Stratospheric Observatory for 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 infall in the clumps. These detections include two clumps embedded in infrared dark clouds. The measured velocity shifts of the absorptions compared to optically thin C¹⁷O (3–2) emission are 0.3–2.8 km s^-1, corresponding to fractions of 3% to 30% of the free-fall velocities of the clumps. The ammonia infall signature is compared with complementary data of different transitions of HCN, HNC, CS, and HCO⁺, which are often used to probe infall because of their blue-skewed line profiles. 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 infall in molecular clumps. Infall rates 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 infall on clump scales is ubiquitous through a wide range of evolutionary stages, from L/M covering about ten to several hundreds.