  (Abridged) Polarization measurements of the Galactic plane at lambda6 cm
probe the interstellar medium (ISM) to larger distances compared to
measurements at longer wavelengths, hence enable us to investigate properties
of the Galactic magnetic fields and electron density. We are conducting a new
lambda6 cm continuum and polarization survey of the Galactic plane covering
10degr < l < 230degr and |b|<5degr. Missing large-scale structures in the U and
Q maps are restored based on extrapolated polarization K-band maps from the
WMAP satellite. The lambda6 cm data are analyzed together with maps at other
bands. We discuss some results for the first survey region, 7degr X 10degr in
size, centered at (l,b)=(125.5degr, 0degr). Two new passive Faraday screens,
G125.6-1.8 and G124.9+0.1, were detected. They cause significant rotation of
background polarization angles but little depolarization. G124.9+0.1 was
identified as a new faint HII region at a distance of 2.8 kpc. G125.6-1.8, with
a size of about 46 pc, has neither correspondence in enhanced Halpha emission
nor a counterpart in total intensity. A model combining foreground and
background polarization modulated by the Faraday screen was developed. Using
this model, we estimated the strength of the ordered magnetic field along the
line of sight to be 3.9 microGauss for G124.9+0.1, and exceeding 6.4 microGauss
for G125.6-1.8. We obtained an estimate of 2.5 and 6.3 mK/kpc for the average
polarized and total synchrotron emissivity towards G124.9+0.1. The synchrotron
emission beyond the Perseus arm is quite weak.

Astrophysics