演講資訊

摘要：

In this talk I will present our new study on the interplay between magnetic field, gravity, and turbulence in the fragmentation process of cores within the filamentary infrared dark cloud G34.43.  We observe the magnetic field (B) morphology across G34.43, traced with thermal dust polarization at 350 micron with an angular resolution of 10" (0.18 pc), and compare with the kinematics obtained from N2H+ across the filament. We derive local velocity gradients from N2H+, tracing motion in the plane of sky, and compare with the observed local B field orientations in the plane of sky. The B field orientations are found to be perpendicular to the long axis of the filament toward the MM1 and MM2 ridge, suggesting that the B field can guide material toward the filament.  Toward MM3, the B field orientations appear more parallel to the filament and aligned with the elongated MM3 core, hinting a different B field role. Besides a large-scale east-west velocity gradient, we find a close alignment between local B field orientations and local velocity gradients toward the MM1/MM2 ridge. This local correlation in alignment supports a scenario where gas motions and B field lines are intertwined. Additionally, this alignment appears to be anti-correlated with total thermal dust emission, showing a tightening alignment with growing emission. We analyze and quantify B field, gravity, turbulence, and their relative importance toward the three cores with various techniques.  We extract all quantities over two scales, a larger clump area at 0.6 pc scale and the smaller core area at 2 pc scale. While we find that gravitational energy, B field, and turbulent pressure all grow systematically from large to small scale for the three cores, we reveal that the ratios among the three constituents develop clearly differently over scale. We propose that this varying relative importance between B field, gravity, and turbulence over scale drives and explains the different fragmentation types seen at sub-pc scale (no fragmentation in MM1; aligned fragmentation in MM2; clustered fragmentation in MM3). We discuss uncertainties, subtleties, and robustness of our conclusion, and we stress the need of a multi-scale joint analysis to understand the dynamics in these systems.