A Sino-German 6 cm polarization survey of the Galactic plane III. The region from 10 degree to 60 degree longitude

TL;DR

This survey at 6 cm maps the Galactic plane's total intensity and polarization, revealing magnetic field structures, turbulence effects, and separating thermal and non-thermal emissions to enhance understanding of Galactic magnetic phenomena.

Contribution

First detailed 6 cm polarization survey of the Galactic plane covering 10° to 60° longitude, with improved zero-level calibration and analysis of magnetic field structures.

Findings

Polarized emission originates within about 4 kpc in the plane.

Polarization patches are due to turbulent magnetic cells.

Faraday Screen's magnetic field exceeds 8 microG.

Abstract

(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.