Tracing cosmic magnetic fields using molecules

Understanding the magnetic field strength and morphology of astrophysical regions is of great importance in understanding their dynamics. There exist a number of methods astronomers can employ to trace magnetic field structures, and each have their own limitations. A promising technique to trace the magnetic field morphology around evolved stars, or on the smallest scales of (high-mass) star forming regions, is (sub-)millimeter spectral line polarization observations. Line (linear) polarization can either arise in association with maser radiative transfer, or alternatively, molecular lines polarize through the Goldreich-Kylafis effect. In both cases, the polarization angle traces the magnetic field with a 90-degree ambiguity. In order to remove this ambiguity, and to estimate the observational viability of particular line polarization measurements, polarized line radiative transfer needs to be employed. In this talk, I present (i) polarized radiative transfer tools that quantify the polarization of maser radiation, (ii) a three-dimensional polarized line radiative transfer tool: PORTAL. PORTAL simulates the emergence of thermal molecular line polarization in astrophysical objects of arbitrary geometry and magnetic field morphology, (iii) A novel polarization mechanism: collisional polarization. Which provides the possibility of directly detecting ambipolar diffusion in disks through the polarization of molecular ions, and I will discuss observations of molecular line polarization around evolved stars and on the smallest scales of (high-mass) star forming region