Observational signatures of helical galactic magnetic fields

We investigate the possibility of reproducing the observed polarization and Faraday rotation properties of spiral galaxies assuming their disks to be filled with regular helical magnetic fields. Both small-scale (< 1 kpc) flux tubes predicted by local hydrodynamicmodels and global, galaxy-scale (several kpc) fields generated by the dynamoprocess 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.