| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| subtitle
| - III. Global magnetic field topology
|
| Title
| - The Westerbork SINGS survey
|
| Date
| |
| has manifestation of work
| |
| related by
| |
| Author
| |
| 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.
|
| article type
| |
| publisher identifier
| |
| Date Copyrighted
| |
| Rights
| |
| Rights Holder
| |
| is part of this journal
| |
| is primary topic
of | |
