OBSERVATIONAL SIGNATURES OF HELICAL GALACTIC MAGNETIC-FIELDS

We investigate the possibility of reproducing the observed polarizatio n and Faraday rotation properties of spiral galaxies assuming their di sks to be filled with regular helical magnetic fields. Both small-scal e (< 1 kpc) flux tubes predicted by local hydrodynamic models and glob al, galaxy-scale (several kpc) fields generated by the dynamo process are considered. The large-scale fields are found to well reproduce the observed regular spiral pattern of polarization B vectors, as well as asymmetries of Faraday rotation and low-frequency polarization, often believed to signify non-axisymmetric or bisymmetric fields.