Unveiling a network of parallel filaments in the Infrared Dark Cloud
  G14.225-0.506
  We present the results of combined NH3(1,1) and (2,2) line emission observed
with the Very Large Array and the Effelsberg 100m telescope of the Infrared
Dark Cloud G14.225-0.506. The NH3 emission reveals a network of filaments
constituting two hub-filament systems. Hubs are associated with gas of
rotational temperature Trot \sim 25 K, non-thermal velocity dispersion ~1.1
km/s, and exhibit signs of star formation, while filaments appear to be more
quiescent (Trot \sim 11 K, non-thermal velocity dispersion ~0.6 km/s).
Filaments are parallel in projection and distributed mainly along two
directions, at PA \sim 10 deg and 60 deg, and appear to be coherent in
velocity. The averaged projected separation between adjacent filaments is
between 0.5 pc and 1pc, and the mean width of filaments is 0.12 pc. Cores
within filaments are separated by ~0.33 pc, which is consistent with the
predicted fragmentation of an isothermal gas cylinder due to the 'sausage'-type
instability. The network of parallel filaments observed in G14.225-0.506 is
consistent with the gravitational instability of a thin gas layer threaded by
magnetic fields. Overall, our data suggest that magnetic fields might play an
important role in the alignment of filaments, and polarization measurements in
the entire cloud would lend further support to this scenario.
