Abstract
Star formation takes place in the high-density regions of molecular clouds where magnetic fields and turbulence are the two main mechanism support- ing molecular clouds against self-gravity. Recent observations of molecular clouds reveal a two-step scenario of star formation that supersonic flows first compress clouds into parsec-scale filaments, and then gravitational bound filaments collapse and fragment into 0.1 pc star-forming cores. Star formation theory and simulation suggest that magnetic fields and turbulence are both important to form the filaments and cores in molecular clouds. The aim of this thesis is to provide an evidence of the interaction between magnetic fields and turbulence in molecular clouds with SMA observations of (1) the CO J = 3–2 polarization and dust polarization observations in NGC 1333 IRAS 4A to reveal a helical structure of magnetic fields in the protostellar outflows at few thousand AU scales, (2) dust polarization observations in six star-forming cores of DR21 filament to investigate the role of magnetic fields during the evolution from filament to cores, and (3) molecular line observations in the six cores to study the interaction between magnetic fields and gas dynamics in the DR21 filament. The observations show that the cores appear to be either-parallel-or-perpendicular to the magnetic fields of filaments, indicating that the parsec-scale magnetic fields play an important role in the formation of cores. However, the alignment break at scales below thousand AU scales, which would be caused by the transformation of gravitational energy to kinematic energy through the process of infall, rotation, or outflow of the cores. Overall, this thesis suggests that magnetic fields are important in regulating the structures of collapsing filaments, and the kinematics arising from gravitational collapse are important in star-forming cores. Therefore, the interaction between magnetic fields and kinematics during the evolution from filament to cores is important in regulating the filaments at few parsec scales and regulating the cores at thousand AU scales.