Context :

Aims : We aim to study polarized short-wavelength emission from the inner Galaxy , which is nearly invisible at long wavelengths because of depolarization .
Information on the diffuse continuum emission at short wavelengths is required to separate Galactic thermal and non-thermal components including existing long-wavelength data .

Methods : We have conducted a total intensity and polarization survey of the Galactic plane at \lambda 6 cm using the Urumqi 25 m telescope for the Galactic longitude range of 10 \degr \leq l \leq 60 \degr and the Galactic latitude range of |b| \leq 5 \degr .
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 \lambda 11 cm survey .

Results : Total intensity and polarization maps are presented with an angular resolution of 9 \aas@@fstack { \prime } 5 and a sensitivity of 1 mK T _ { B } and 0.5 mK T _ { B } in total and polarized intensity , respectively .
The \lambda 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 \mu G. 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 \lambda 6 cm is about 60 % in the plane .

Conclusions : The Sino-German \lambda 6 cm polarization survey of the inner Galaxy provides new insights into the properties of the magnetized interstellar medium for this very complex Galactic region , which is Faraday thin up to about 4 kpc in the Galactic plane .
Within this distance polarized patches were identified as intrinsic structures related to turbulent Galactic magnetic fields for spatial scales from 20 ( d/4 kpc ) to 200 ( d/4 kpc ) pc