Browsing by Author "Tahani, Mehrnoosh"

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    The Large-Scale Structure of Magnetic Fields Associated with Filamentary Molecular Clouds
    (2019-01-22) Tahani, Mehrnoosh; Plume, René; Brown, Jo Anne C.; Houde, Martin; Hobill, David W.; Knudsen, David J.; Behjat, Laleh
    Magnetic fields pervade the interstellar medium and are believed to be important in the star formation process. However, probing magnetic fields in these star-forming regions is challenging. I propose and demonstrate a new method, using Faraday rotation measurements, to probe the direction and magnitude of the magnetic field along the line-of-sight in and around filamentary molecular clouds that are forming stars. Using my method, which utilises rotation measure data from the literature, a chemical evolution code, and extinction maps to estimate electron column density, I determine the magnetic field in four nearby molecular clouds: Orion A, Orion B, Perseus, and California. I find that my method produces results in agreement with the limited number of available Zeeman measurements. Using the magnetic field results from this new method, I find that the line-of-sight magnetic field on either side of the California and Orion A filaments has opposing magnetic field directions. Three theoretical magnetic field morphologies can explain this change of direction across filaments: toroidal, helical, and bow morphologies. I investigate these three models by combining my results with those of Planck observations to determine the 3D magnetic field structure in Orion A. I find that of the three possible morphologies, toroidal is the least probable whereas the bow morphology is the most natural. To investigate these morphologies further, I use magnetohydrodynamics simulations to simulate filamentary molecular clouds and their magnetic field evolution. I use different initial parameters to see if the magnetic field lines can become twisted around a rotating filament, potentially forming helical fields. I find that helical fields are not easily generated in these scenarios.