The Sino-German polarization survey of the Galactic plane has used the Urumqi 25-m telescope of the Xinjiang Astronomical Observatory to conduct continuum observations of the Galactic plane at 6 cm wavelength. It took about 10 years to finish the project successfully.

The survey is an important result of a collaboration between the Max Planck Society in Germany and the Chinese Academy of Sciences where a partner group of the Max Planck Institute for Radio Astronomy in Bonn was established at the National Astronomical Observatory in Beijing.

Large-scale diffuse polarized emission was observed in order to study the magnetic field of the Milky Way. Several large discrete objects were investigated, and two new supernova remnants (SNRs) were discovered from the Urumqi Galactic plane survey.

Figure 1:  Two new SNRs discovered by using the 25-m telescope of XAO.

Prof. JinLin Han, head of the "compact objects and diffuse medium" group of National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS), and Prof. Richard Wielebinski, Director Emeritus at Max-Planck-Institute for Radioastronomy (MPIfR), initiated the cooperative study on the Galactic magnetism in 2001. The 6cm survey using the Urumqi 25-m telescope of XAO has a similar angular resolution as the 21cm survey of the Effelsberg 100-m telescope of MPIfR. The synergy of these surveys can definitely advance the understanding of the Galactic interstellar medium.

In the general cooperation framework between Max-Planck Society and Chinese Academy of Sciences, and the National Scientific Foundation of China, the Partner group of MPIfR at NAOC supported the construction of the receiving system at MPIfR and installed it on the 25-m telescope. With the help of the local staff at XAO, the Partner group made observations for about 4500 hours.

The survey covered the northern band of the Milky Way with Galactic longitude between 10 and 230 degrees, and Galactic latitude between -5 and 5 degrees, an area of 2200 square degrees. This survey is the highest frequency polarization survey ever made with earth-based instruments.

The Galactic interstellar medium, consisting of magnetic fields, electrons, atomic gas and other components, can significantly influence polarization measurements at low frequencies. Therefore the 6cm survey can detect magnetic fields from much larger distances than other low frequency surveys. The Partner group studied the properties of large-scale diffuse emission based on the observations. Moreover they were able to map large discrete objects which cannot be observed by big telescopes, such as dense ionized clouds called HII regions and residuals of exploded stars, the Supernova Remnants, SNRs. A handful of peculiar thermal clumps with very strong regular magnetic fields, called Faraday Screens, were also detected. The 6cm data are very essential to establish the spectra of Galactic sources.

The Partner group found two miss-identified SNRs G166.2+2.5 and G192.8-1.1, which turn out to be thermal clouds, and discovered two very faint new weak SNRs G178.2-4.2 and G25.1-2.3 with sizes of about 1 degree. These are the first SNRs discovered using a Chinese radio telescopes. Note that there are only about 270 known SNRs up till now.

"As a result of our survey work five PhD degrees have been completed in our group", says Prof. JinLin Han, the leader of the partner group in Beijing. "Our cooperaton has considerably strengthened radio astronomy in China. The aim of the Partner Group has been fully achieved."

The partner group has made 24 publications since 2002, most of which are in the renowned journal Astronomy & Astrophysics. Two of the papers were highlighted by A&A. With this project lots of experience on radio continuum observations has been gained and progress on receiver technology has also been made for Chinese astronomers. Five PhDs have been awarded from the project.

"Through visits to the participating institutes many personal contacts were built up between astronomers and technicians in both countries", says Prof. Richard Wielebinski from Max-Planck-Institut für Radioastronomie in Bonn, who established the partner group. "The German side received understanding of cooperation with Chinese researchers. The good cooperation that was started in the framework of the Partner Group will continue on a personal basis."

Figure 2:  25m radio telescope of Urumqi Astronomical Observatory, CAS. Credit: Maria Rioja (MPIfR).

Magnetic Fields in Galaxies: MPG Partner group of Prof. JinLin Han at National Astronomical Observatories, Beijing.

The foundation of this Partner Group goes back on a decision of the Max-Planck-Gesellschaft (MPG) dated 09.11.2000. The proposal was to cooperate in the research of magnetic fields in galaxies in general, with a special emphasis on the study of the magnetic fields in the Milky Way.

The most important contribution of the Max-Planck-Institut für Radioastronomie (MPIfR) was the construction of a state of art receiver at 6-cm wavelength with a polarimeter to be used in survey observations of the Galactic plane at the 25-m Nanshan radio telescope in Urumqi (P.R. China). This radio telescope had the advantage to be located at the altitude of 2000-m that allows better high frequency observations in clear weather. In early discussions support in the installation of the polarimetry receiver and in observing techniques was offered by the MPIfR.

In the process of implementing the observations it was necessary to include the feed horn antenna and scanning software in the Urumqi telescope system, again a contribution by the MPIfR. The gross of the observation and the data reduction was carried out by students of Prof. JinLin Han based in the National Astronomical Observatories (NAO) in Beijing. Prof. Wolfgang Reich led a team of MPIfR staff that made the initial tests and advised in the observations of the survey. The final preparations of scientific papers were carried out at the MPIfR in Bonn and the NAO Beijing.

Additional Information:

Sino-German 6cm Polarization Survey (JPEG, 31 MByte). Complete area in total intensity, Stokes Q and U and polarized intensity.

Partner Group of MPI für Radioastronomie at National Astronomical Observatories, Chinese Academy of Sciences (CAS).

Urumqi Radio Observatory.

Sino-German Centre for Research Promotion of DFG and CAS in Beijing.

Contact:

Prof. Richard Wielebinski,
Head of the Partner Group in Germany,
Max-Planck-Institut für Radioastronomie, Bonn.
Telefon: 0228-525-300
E-mail: rwielebinski at mpifr-bonn.mpg.de