Unveiling a network of parallel filaments in the infrared dark cloud G14.225-0.506

摘要

We present the results of combined NH_3 (1,1) and (2,2) line emission observed with the Very Large Array and the Effelsberg 100 m telescope of the infrared dark cloud G14.225-0.506. The NH_3 emission reveals a network of filaments constituting two hub-filament systems. Hubs are associated with gas of rotational temperature T _(rot) ～ 15 K, non-thermal velocity dispersion σ_(NT) ～ 1 km s~(-1), and exhibit signs of star formation, while filaments appear to be more quiescent (T _(rot) ～ 11 K and σ_(NT) ～ 0.6 km s~(-1)). Filaments are parallel in projection and distributed mainly along two directions, at P.A. ～ 10° and 60°, and appear to be coherent in velocity. The averaged projected separation between adjacent filaments is between 0.5 pc and 1 pc, and the mean width of filaments is 0.12 pc. Cores within filaments are separated by ～0.33 ± 0.09 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.