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Date and Time of the Query: 2019-06-18 T12:20:29 PDT
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For refcode 2010A&A...514A..42B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2010A&A...514A..42B The Westerbork SINGS survey. III. Global magnetic field topology Braun, R.; Heald, G.; Beck, R. Abstract. A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS) galaxies was observed with the Westerbork Synthesis Radio Telescope (WSRT) at 1300--1760 MHz. In Paper II of this series, we described sensitive observations of the linearly polarized radio continuum emission in this WSRT-SINGS galaxy sample. Large-scale magnetic field structures of two basic types are found: (a) disk fields with a spiral topology in all detected targets; and (b) circumnuclear, bipolar outflow fields in a subset. Here we explore the systematic patterns of azimuthal modulation of both the Faraday depth and the polarized intensity and their variation with galaxy inclination. A self-consistent and fully general model for both the locations of net polarized emissivity at 1--2 GHz frequencies and the global magnetic field topology of nearby galaxies emerges. Net polarized emissivity is concentrated into two zones located above and below the galaxy mid-plane, with the back-side zone suffering substantial depolarization (by a factor of 4--5) relative to the front-side zone in its propagation through the turbulent mid-plane. The field topology which characterizes the thick-disk emission zone, is in all cases an axisymmetric spiral with a quadrupole dependence on height above the mid-plane. The front-side emission is affected by only mild dispersion (10's of rad m^-2^) from the thermal plasma in the galaxy halo, while the back-side emission is affected by additional strong dispersion (100's of rad m^-2^) from an axi-symmetric spiral field in the galaxy mid-plane. The field topology in the upper halo of galaxies is a mixture of two distinct types: a simple extension of the axisymmetric spiral quadrupole field of the thick disk and a radially directed dipole field. The dipole component might be a manifestation of (1) a circumnuclear, bipolar outflow; (2) an in situ generated dipole field; or (3) evidence of a non-stationary global halo. Key words: ISM: magnetic fields, galaxies: magnetic fields, radio continuum: galaxies
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