Investigating the structure and fragmentation of a highly filamentary
  IRDC
  We present 3.7 arcsec (~0.05 pc) resolution 3.2 mm dust continuum
observations from the IRAM PdBI, with the aim of studying the structure and
fragmentation of the filamentary Infrared Dark Cloud G035.39-00.33. The
continuum emission is segmented into a series of 13 quasi-regularly spaced
(~0.18pc) cores, following the major axis of the IRDC. We compare the spatial
distribution of the cores with that predicted by theoretical work describing
the fragmentation of hydrodynamic fluid cylinders, finding a significant (a
factor of ~8) discrepancy between the two. Our observations are consistent with
the picture emerging from kinematic studies of molecular clouds suggesting that
the cores are harboured within a complex network of independent sub-filaments.
This result emphasizes the importance of considering the underlying physical
structure, and potentially, dynamically important magnetic fields, in any
fragmentation analysis. The identified cores exhibit a range in (peak)
beam-averaged column density ($3.6{\rm x}10^{23}{\rm cm}^{-2}<N_{H,c}<8.0{\rm
x}10^{23}{\rm cm}^{-2}$), mass ($8.1M_{\odot}<M_{c}<26.1M_{\odot}$), and number
density ($6.1{\rm x}10^{5}{\rm cm}^{-3}<n_{H, c, eq}<14.7{\rm x}10^{5}{\rm
cm}^{-3}$). Two of these cores, dark in the mid-infrared,
centrally-concentrated, monolithic (with no traceable substructure at our PdBI
resolution), and with estimated masses of the order ~20-25$M_{\odot}$, are good
candidates for the progenitors of intermediate-to-high-mass stars. Virial
parameters span a range $0.2<\alpha_{\rm vir}<1.3$. Without additional support,
possibly from dynamically important magnetic fields with strengths of the order
230$\mu$G<B<670$\mu$G, the cores are susceptible to gravitational collapse.
These results may imply a multilayered fragmentation process, which
incorporates the formation of sub-filaments, embedded cores, and the
possibility of further fragmentation.
