Three-dimensional observations of interstellar magnetic fields

Magnetic fields pervade the interstellar medium and are important in the star-formation process. However, probing magnetic fields of star-forming regions is challenging. In this talk, I will discuss our research on the 3D morphology of magnetic fields in star-forming molecular clouds. We first developed a novel technique based on Faraday rotation measurements to determine the line-of-sight strength and direction of magnetic fields associated with molecular clouds. We applied our technique to four relatively nearby filamentary molecular clouds. For three of these clouds, we found that the line-of-sight magnetic field reverses across these clouds. We then incorporated these line-of-sight and Planck's plane-of-sky magnetic field observations along with models to study the 3D magnetic field morphology of the Orion A cloud. Recently, we determined the complete 3D magnetic field vectors (with signed directions), using large-scale Galactic magnetic field models and our line-of-sight maps for the Perseus and Orion A molecular clouds. At the end, I will briefly mention some of our ongoing research on the role of magnetic fields in the star-formation process.