The converging gas flow around the infrared dark cloud G28.37

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
² Harvard-Smithsonian Center for Astrophysics, 160 Garden St, Cambridge, MA 02420, USA
³ Department of Astronomy, Xiamen University, Zengcuoan West Road, Xiamen 361005, PR China
⁴ ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands
⁵ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁶ Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 September 2025
Accepted: 17 December 2025

Abstract

Context. How dense clouds and star-forming regions form out of the dynamical interstellar medium is at the heart of star formation research.

Aims. The G28.37+0.07 star-forming region is a prototypical infrared dark cloud (IRDC) located at the interface of a converging gas flow. This study characterizes the properties of this dynamic gas flow.

Methods. Combining data from the Northern Extended Millimeter Array (NOEMA) with single-dish data from the IRAM 30 m observatory, we mapped large spatial scales (~81 pc²) at high angular resolution (7.0″ × 2.6″ corresponding ~2.3×10⁴ au or ~0.1 pc) down to core scales. The spectral setup in the 3 mm band covers many spectral lines as well as the continuum emission.

Results. The data clearly reveal the proposed west–east converging gas flow in all observed dense gas tracers. We estimate a mass-flow rate along that flow around 10⁻³ M_⊙ yr⁻¹. Comparing these west–east flow rates to infall rates toward sources along the line of sight, the gas flow rates are roughly a factor of 25 greater than those along the line of sight (roughly perpendicular to the west–east flow). This confirms the dominance of longitudinal motions along the converging gas flow in this region. For comparison, in the main north–south IRDC formed by the west–east converging gas flow, infall rates along the line of sight are about an order of magnitude greater than those along the west–east flow. In addition to the kinematic analysis, a comparison of CH₃ CN-derived gas temperatures with Herschel- derived dust temperatures typically show higher gas temperatures toward high-density sources. We discuss whether mechanical heating from the conversion of the flow’s kinetic energy into thermal energy may explain some of the observed temperature differences.

Conclusions. Our analysis of the G28.37+0.07 converging gas flow shows that such structures can indeed form and feed typical highmass star-forming regions in the Milky Way. The differences between flow rates along the converging flow, perpendicular to it, and toward the sources at the IRDC center indicate that at the interfaces of converging gas flows – where most of the active star formation takes place – originally more directed gas flows can convert into multidirectional infall motions.