Fragmentation and kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11-0.12

Abstract

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 0.2 km s-1. 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 30 m telescope. We recover the star-forming cores at 3.2 mm continuum, while in N2H+ they appear at the peaks of extended structures. The mean projected spacing between N2H+ 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 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.