The potential of dust polarization measurements : on the observability of magnetic field structures in star-forming regions

This work aims to evaluate the potential of polarization measurements to determine the underlying magnetic field morphology involved in the star formation process. Dust grains partially align with the direction of the magnetic field. Hence, light will gain polarization with respect to the magnetic field direction. Revealing the magnetic field morphology with the help of polarization measurements requires continuum dust RT calculations in arbitrary 3D geometries taking the impact of partially aligned dust grains into account. Here, we follow the approach to post-process complex magnetic field, temperature, and density distributions from models and MHD simulations to create synthetic polarization maps. To constrain the role of magnetic fields in star formation we developed the 3D RT code POLARIS suitable for dust heating and polarization simulations. The code solves the radiative transfer problem combined with the polarization effects of dichroic extinction and thermal re-emission. Here, we combine RT and polarization algorithms with state of the art dust grain alignment theories. The optical properties of the dust materials are pre-calculated by approximating them on the basis of the laboratory data. This approach allows to constrain the impact of grain alignment on polarization pattern. We start with a spherical density distribution in combination with magnetic field model and investigate, if projection effects and low inclination angles allow to distinguish between different field morphologies. Then, we compare observations of circumstellar disks with synthetic polarization maps. Later, we create polarization maps of a cloud model and analyze the unique patterns associated with different grain alignment theories. Finally, we post-process a MHD collapse simulation. Here, we determine the potential of multi-wavelength polarization measurements to probe distinct characteristic parts of a larger connected magnetic field structure.


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