Fragmentation and Kinematics of dense molecular cores in the filamentary
  infrared-dark cloud G011.11-0.12
  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 3.2mm 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" and velocity resolution of 0.2km s$^{-1}$.
These data are presented in concert with recent {\em 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 30m telescope. We recover
the star-forming cores at 3.2mm 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 0.18pc, 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 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.
