A Sino-German 6 cm polarization survey of the Galactic plane III. The
  region from 10 degree to 60 degree longitude
  (Abridged) We have conducted a total intensity and polarization survey of the
Galactic plane at 6 cm using the Urumqi 25 m telescope for the Galactic
longitude range of 10 deg<l<60 deg and the Galactic latitude range of |b|<5
deg. Missing absolute zero levels of Stokes U and Q maps were restored by
extrapolating the WMAP five-year K-band polarization data. For total
intensities we recovered missing large-scale components by referring to the
Effelsberg 11 cm survey. Total intensity and polarization maps are presented
with an angular resolution of 9.5 arcmin and a sensitivity of 1 mK and 0.5 mK
in total and polarized intensity, respectively. The 6 cm polarized emission in
the Galactic plane originates within about 4 kpc distance, which increases for
polarized emission out of the plane. The polarization map shows "patches",
"canals" and "voids" with no correspondence in total intensity. We attribute
the patches to turbulent magnetic field cells. Canals are caused by abrupt
variation of polarization angles at the boundaries of patches rather than by
foreground Faraday Screens. The superposition of foreground and Faraday Screen
rotated background emission almost cancels polarized emission locally, so that
polarization voids appear. By modelling the voids, we estimate the Faraday
Screen's regular magnetic field along the line-of-sight to be larger than about
8 microG. We separated thermal (free-free) and non-thermal (synchrotron)
emission according to their different spectral indices. The spectral index for
the synchrotron emission was based on WMAP polarization data. The fraction of
thermal emission at 6 cm is about 60% in the plane.
