Interferometric mapping of magnetic fields in star-forming regions

Magnetic fields are thought to play a significant role in all stages of star formation. However, there are few observations that measure magnetic fields at the relevant scale for the star formation process. In this thesis, I present the results from a survey of linear polarization in molecular cores at 1.3 mm wavelength with the BIMA millimeter interferometer. The linear polarization from dust emission and the CO J = 2 → 1 line are observed simultaneously, providing the magnetic field directions in the plane of sky. The observations achieve angular resolution up to 2″, which is more than 5 times better than previous single-dish observations. The improvement in angular resolution allows me to investigate detailed magnetic field morphology and obtain reliable values for the dispersion of the polarization angles. The analysis in the dispersion of the polarization angles further provides estimates for the magnetic field strengths in the plane of sky, the upper limit of the mass-to-flux ratios, and the turbulent to magnetic energy ratio.; I obtained extended dust polarization maps of W51 e1/e2, NGC 2024 FIR 5, DR21(OH), and NGC 1333 IRAS 4A, and CO polarization map of DR21(OH). The magnetic field morphologies in these cores are consistent with the predictions of star formation theories: W51 e1/e2 has a uniform magnetic field parallel to the minor axis of the double cores; NGC 2024 FIR 5 and NGC 1333 IRAS 4A show morphologies similar to an hour-glass shape; DR21(OH) has a toroidal magnetic field morphology, perhaps due to the mutual revolution of its two components.; The dispersion of the polarization angle is generally small except in DR21(OH), suggesting that the magnetic field probably dominates turbulence. Even for DR21(OH), its turbulent energy is only ∼40% of its magnetic energy. The magnetic field strength in the plane of the sky, obtained from the Chandrasekhar-Fermi method, ranges from 0.8 mG to 3.5 mG in these cores. The upper limit of the mass-to-flux ratios are in the supercritical regime for W51 e1/e2 and DR21(OH), and NGC 2024 FIR 5 and NGC 1333 IRAS 4A are most likely to be subcritical cores.; In addition, it is generally found in my sample that the degree of dust polarization decreases toward the high intensity regions and toward the center of the core. These results suggest that the dust polarization efficiency decreases toward the regions with high density and/or high optical depth.