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 N _ { 2 } H ^ { + } ( 1-0 ) line to trace the core kinematics with an angular resolution of 2 ^ { \prime \prime } and velocity resolution of 0.2 km s ^ { -1 } .
These data are presented in concert with recent Herschel results , single-dish N _ { 2 } H ^ { + } ( 1-0 ) data , SABOCA 350 \mu m continuum data , and maps of the C ^ { 18 } O ( 2-1 ) transition obtained with the IRAM 30 m telescope .
We recover the star-forming cores at 3.2 mm continuum , while in N _ { 2 } H ^ { + } they appear at the peaks of extended structures .
The mean projected spacing between N _ { 2 } H ^ { + } emission peaks is 0.18 pc , consistent with simple isothermal Jeans fragmentation .
The 0.1 pc-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 N _ { 2 } H ^ { + } 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 N _ { 2 } H ^ { + } velocity components are detected , one of which has no counterpart in C ^ { 18 } O .
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 .