A Sino-Germanλ6 cm polarization survey of the Galactic plane

Abstract

Aims. We study polarized short-wavelength emission from the inner Galaxy, which is nearly invisible at long wavelengths because of depolarization. We attempt to obtain information on the diffuse continuum emission at short wavelengths to help us to separate Galactic thermal and non-thermal components. Methods. We conducted a total intensity and polarization survey of the Galactic plane at λ6 cm using the Urumqi 25 m telescope for the Galactic longitude range of 10 • ≤ l ≤ 60 • and the Galactic latitude range of |b| ≤ 5 • . 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 λ11 cm survey. Results. Total intensity and polarization maps are presented with an angular resolution of 9. 5 and a sensitivity of 1 mK T B and 0.5 mK T B in total and polarized intensity, respectively. The λ6 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 in the polarization angles at the boundaries of patches rather than by foreground Faraday screens. The superimposition of foreground and Faraday screen rotated background emission almost cancels the polarized emission locally, such 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 μG. We separated thermal (free-free) and non-thermal (synchrotron) emission according to their different spectral indices. The spectral index for the synchrotron emission is based on WMAP polarization data. The fraction of thermal emission at λ6 cm is about 60% in the plane. Conclusions. The Sino-German λ6 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 are identified as intrinsic structures related to turbulent Galactic magnetic fields of spatial scales from 20(d/4 kpc) to 200(d/4 kpc) pc.

Newλ6 cm andλ11 cm observations of the supernova remnant CTA 1

“…In this paper, we present new λ6 cm and λ11 cm observations of CTA 1, which is one of the targets of a campaign to map large northern sky SNRs at λ6 cm. This project is part of the Sino-German λ6 cm polarisation survey of the Galactic plane Gao et al 2010;Sun et al 2011;Xiao et al 2011;Gao et al 2011). Results on some large SNRs have been already reported, such as G65.2+5.7 (Xiao et al 2009), the Cygnus Loop (Sun et al 2006), HB 3 (Shi et al 2008), G156.2+5.7 (Xu et al 2007), and S 147 (Xiao et al 2008).…”

Discovery of a new supernova remnant G150.3+4.5

“…There are also some individual discoveries, although not many. The SinoGerman λ6 cm polarization survey of the Galactic plane 1 (Sun et al 2007(Sun et al , 2011a; Gao et al 2010;Xiao et al 2011) conducted by the Urumqi 25-m radio telescope provides a good hunting ground for discovering new Galactic SNRs. Gao et al (2011) identified two new faint SNRs G25.1−2.3 and G178.2−4.2.…”

A Sino-Germanλ6 cm polarization survey of the Galactic plane

“…It covers 10 • ≤ ≤ 230 • in Galactic longitude and |b| ≤ 5 • in Galactic latitude Gao et al 2010;Sun et al 2011;Xiao et al 2011). The Urumqi λ6 cm polarization system is suitable for observations of large and faint SNRs.…”