  Deep scaled array VLA 20 and 6cm observations including polarization of 19
Virgo spirals are presented. This sample contains 6 galaxies with a global
minimum of 20cm polarized emission at the receding side of the galactic disk
and quadrupolar type large-scale magnetic fields. In the new sample no
additional case of a ram-pressure stripped spiral galaxy with an asymmetric
ridge of polarized radio continuum emission was found. In the absence of a
close companion, a truncated HI disk, together with a ridge of polarized radio
continuum emission at the outer edge of the HI disk, is a signpost of ram
pressure stripping. 6 out of the 19 observed galaxies display asymmetric 6cm
polarized emission distributions. Three galaxies belong to tidally interacting
pairs, two galaxies host huge accreting HI envelopes, and one galaxy had a
recent minor merger. Tidal interactions and accreting gas envelopes can lead to
compression and shear motions which enhance the polarized radio continuum
emission. In addition, galaxies with low average star formation rate per unit
area have a low average degree of polarization. Shear or compression motions
can enhance the degree of polarization. The average degree of polarization of
tidally interacting galaxies is generally lower than expected for a given
rotation velocity and star formation activity. This low average degree of
polarization is at least partly due to the absence of polarized emission from
the thin disk. Ram pressure stripping can decrease whereas tidal interactions
most frequently decreases the average degree of polarization of Virgo spiral
galaxies. We found that moderate active ram pressure stripping has no influence
on the spectral index, but enhances the global radio continuum emission with
respect to the FIR emission, while an accreting gas envelope can but not
necessarily enhances the radio continuum emission with respect to the FIR
emission.
