How dense clouds and star-forming regions form out of the dynamical interstellar medium is at the heart of star formation research. 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. 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. 3times 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. The data clearly reveal the proposed west-east converging gas flow in all observed dense gas tracers. We estimate a mass-flow rate along -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 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 CH₃CN-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. Our analysis of the G28. 37+0. 07 converging gas flow shows that such structures can indeed form and feed typical high-mass 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.
Beuther et al. (Tue,) studied this question.