Speaker: Sui Ann Mao

Title: Magnetic Fields in the Thick Disk of the Milky Way

Abstract: We present a study of the magnetic field and the turbulence in the magneto-ionic medium in the thick disk of the Milky Way, carried out using Faraday rotation of 813 polarized extragalactic radio sources at |b| > 77°. The mean rotation measure (RM) towards the north Galactic pole is consistent with zero, implying that no coherent vertical magnetic field is measured. Positive mean RM towards the south Galactic pole indicates a coherent vertical magnetic field directed towards us. Assuming that diffused interstellar free electrons is the Faraday rotating screen, we derived a vertical magnetic field strength of 0.32 ± 0.02 µG towards the south Galactic pole. If the measured vertical magnetic field were global, then the observed field geometry is inconsistent with a pure dipole / quadrupole field model. The difference of the mean RM measured towards the north and the south Galactic poles could potentially be a result of viewing through two magnetized shells in the vicinity of the sun that are responsible for producing the strongly polarized North Polar Spur at radio wavelengths. The existence of a thick disk field of opposite parity to the thin disk field is also a plausible explanation of the observed RM pattern at high Galactic latitudes.

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