2015A&A...573A.119R

We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC) G011.11-0.12 containing young, star-forming cores. In addition to the 3.2 mm continuum emission from cold dust, we map this region in the N₂H⁺(1-0) line to trace the core kinematics with an angular resolution of 2" and velocity resolution of 0.2km/s. These data are presented in concert with recent Herschel results, single-dish N₂H⁺(1-0) data, SABOCA 350 µm continuum data, and maps of the C¹⁸O (2-1) transition obtained with the IRAM 30m telescope. We recover the star-forming cores at 3.2mm continuum, while in N₂H⁺ they appear at the peaks of extended structures. The mean projected spacing between N₂H⁺ emission peaks is 0.18pc, consistent with simple isothermal Jeans fragmentation. The 0.1pc-sized cores have low virial parameters on the criticality borderline, while on the scale of the whole region, we infer that it is undergoing large-scale collapse. The N₂H⁺ linewidth increases with evolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of all tracers are in excellent agreement, except in the starless region where two N₂H⁺ velocity components are detected, one of which has no counterpart in C¹⁸O. We suggest that gas along this line of sight may be falling into the quiescent core, giving rise to the second velocity component, possibly connected to the global collapse of the region.