What is controlling the fragmentation process in the Infrared Dark Cloud
  G14.225-0.506? Differet level of fragmentation in twin hubs
  We present observations of the 1.3 mm continuum emission toward hub-N and
hub-S of the infrared dark cloud G14.225-0.506 carried out with the
Submillimeter Array, together with observations of the dust emission at 870 and
350 microns obtained with APEX and CSO telescopes. The large scale dust
emission of both hubs consists of a single peaked clump elongated in the
direction of the associated filament. At small scales, the SMA images reveal
that both hubs fragment into several dust condensations. The fragmentation
level was assessed under the same conditions and we found that hub-N presents 4
fragments while hub-S is more fragmented, with 13 fragments identified. We
studied the density structure by means of a simultaneous fit of the radial
intensity profile at 870 and 350 microns and the spectral energy distribution
adopting a Plummer-like function to describe the density structure. The
parameters inferred from the model are remarkably similar in both hubs,
suggesting that density structure could not be responsible in determining the
fragmentation level. We estimated several physical parameters such as the level
of turbulence and the magnetic field strength, and we found no significant
differences between these hubs. The Jeans analysis indicates that the observed
fragmentation is more consistent with thermal Jeans fragmentation compared with
a scenario that turbulent support is included. The lower fragmentation level
observed in hub-N could be explained in terms of stronger UV radiation effects
from a nearby HII region, evolutionary effects, and/or stronger magnetic fields
at small scales, a scenario that should be further investigated.
