Determine 3-dimensional Interstellar Magnetic Field via Spectral-line Polarization Observations

Speaker: Tao-Chung Ching (NRAO) In Person and zoom 

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Spectral-line polarization observations of Zeeman effect and Goldreich-Kylafis effect can probe interstellar magnetic fields with velocity information that is not available for continuum polarization observations such as dust thermal emission or synchrotron emission. Zeeman effect of circular polarization is the only direct method to measure line-of-sight magnetic field strength in interstellar medium, and Goldreich-Kylafis effect of linear polarization reveals the plane-of-sky magnetic field structure. Here I present the multi-beam polarization calibration and Zeeman observations of the FAST telescope and ALMA observations of CO (2-1) Goldreich-Kylafis effect. The curl of the magnetic field strength on the plane of sky inferred from CO polarization and the electronic current inferred from CO total emission along the line of sight satisfy Ampère's law in Maxwell's equations to determine the magnetic field direction on the plane of sky. The combination of spectral-line polarization surveys of Zeeman effect and Goldreich-Kylafis effect thus provides a potential to map the 3-dimensional magnetic field structure in 3-dimensional interstellar space.