Evolution of the Hub-filament Structures in IC 5146 in the Context of the Energy Balance of Gravity, Turbulence, and Magnetic Field

Abstract

We present the results of 850 mu m polarization and (CO)-O-18 (3 - 2) line observations toward the western hub-filament structure (W-HFS) of the dark Streamer in IC 5146 using the James Clerk Maxwell Telescope SCUBA-2/POL-2 and HARP instruments. We aim to investigate how the relative importance of the magnetic field, gravity, and turbulence affects core formation in HFS by comparing the energy budget of this region. We identified four 850 mu m cores and estimated the magnetic field strengths (B (pos)) of the cores and the hub and filament using the Davis-Chandrasekhar-Fermi method. The estimated B (pos) is similar to 80 to 1200 mu G. From Wang et al., B (pos) of E-47, a core in the eastern hub (E-hub), and E-hub were reestimated to be 500 and 320 mu G, respectively, with the same method. We measured the gravitational (E (G)), kinematic (E (K)), and magnetic energies (E (B)) in the filament and hubs and compared the relative importance among them. We found that an E (B)-dominant filament has aligned fragmentation type, while E (G)-dominant hubs show no and clustered fragmentation types. In the E (G) dominant hubs, it seems that the portion of E (K) determines whether the hub becomes to have clustered (the portion of E (K) similar to 20%) or no fragmentation type (similar to 10%). We propose an evolutionary scenario for the E- and W-HFSs, where the HFS forms first by the collision of turbulent flows, and then the hubs and filaments can go into various types of fragmentation depending on their energy balance of gravity, turbulence, and magnetic field.