Filaments of Cygnus X

We also re-extract filaments at the resolution of the Planck 353GHz dust emission map to study their relationship with the B-field. The filaments in Cygnus X have a typical width of 0.5pc. More than 93% of high-mass cores (>=20M_Ssun}_) are located on filaments.

The core mass function constructed from the cores on the filaments (onCMF) shows a power-law in the high-mass end (>10M_Ssun}_) with a slope of -2.30, whereas the high-mass end of the CMF derived from the cores outside the filaments (outCMF) has a much steeper power-law distribution with a slope of -2.83. The core mass corresponding to the peak of onCMF is much less than the Bonner-Ebert mass but that corresponding to the peak of outCMF is well comparable to the Bonner-Ebert mass.

Filaments re-extracted from the column density map smoothed to an angular resolution identical to the Planck 353GHz map are mostly perpendicular to the B-field, except that those of lowest column densities are parallel to the B-field. The transition from parallel to perpendicular occurs at a column density equivalent to AV=10mag. Most prominent filamentary gas structures and high-mass cores appear to be preferentially located along the boundaries of HII regions or at the intersections of multiple HII regions.

The filaments close to the HII region boundaries show a steeper column density profile on the side toward the HII region compared to that on the opposite side. The formation of more massive cores has a stronger dependence on filaments, and the latter may provide a mass reservoir for the former to grow in mass via accretion. The B-field plays a crucial role in filament formation, and the type O mode where filaments form at the tip of converging flows along an oblique MHD shock front may be prevalent in Cygnus X. In this context, expanding HII regions in the complex induces shocks which compress the surrounding gas, creating inhomogeneity and dense clumps, and forming filaments.

The global picture of filaments, cores, and star formation in Cygnus X is apparently consistent with the bubble-filament paradigm proposed in the literature.