Issue |
A&A
Volume 463, Number 3, March I 2007
|
|
---|---|---|
Page(s) | 993 - 1007 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20066001 | |
Published online | 19 December 2006 |
A Sino-German
6 cm polarization survey of the Galactic plane
I. Survey strategy and results for the first survey region
1
National Astronomical Observatories, Chinese Academy of Sciences, Jia-20 Datun Road, Chaoyang District, Beijing 100012, PR China e-mail: [xhsun;hjl;swb]@bao.ac.cn
2
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [wreich;preich;rwielebinski;efuerst]@mpifr-bonn.mpg.de
Received:
10
July
2006
Accepted:
10
November
2006
Aims.Polarization measurements of the Galactic plane at λ6 cm probe the interstellar medium (ISM) to larger distances compared to measurements at longer wavelengths, enabling us to investigate properties of the Galactic magnetic fields and electron density.
Methods.We are conducting a new λ6 cm continuum and polarization
survey of the Galactic plane covering and
. Missing large-scale structures in the U and Q maps
are restored based on extrapolated polarization K-band maps from the
WMAP satellite. The λ6 cm data are analyzed together with maps
in other bands.
Results.
We discuss some results for the first survey region,
in size, centered at
.
Two new passive Faraday screens, G125.6-1.8 and G124.9+0.1, were
detected. They cause significant rotation of background polarization angles
but little depolarization. G124.9+0.1 was identified as a new faint HII region at a distance of 2.8 kpc. G125.6-1.8, with a size of about 46 pc, has
neither a counterpart in enhanced Hα emission nor in
total intensity. A model combining foreground and background polarization
modulated by the Faraday screen was developed. Using this model, we estimated
the strength of the ordered magnetic field along the line of sight to be
3.9 μG for G124.9+0.1, and exceeding 6.4 μG for G125.6-1.8. We
obtained an estimate of 2.5 and 6.3 mK kpc-1 for the average polarized
and total synchrotron emissivity towards G124.9+0.1. The synchrotron
emission beyond the Perseus arm is quite weak.
A spectral curvature previously reported for SNR G126.2+1.6 is
ruled out by our new data, which prove a straight spectrum.
Conclusions.The new λ6 cm survey will play an important role in improving the understanding of the properties of the magneto-ionic ISM. The magnetic fields in HII regions can be measured. Faraday screens with very low electron densities but large rotation measures were detected indicating strong and regular magnetic fields in the ISM. Information about the local synchrotron emissivity can be obtained.
Key words: surveys / polarization / radio continuum: general / methods: observational / ISM: magnetic fields / ISM: supernova remnants
© ESO, 2007
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