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Astron. Astrophys. 350, 447-456 (1999)


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Polarimetric structure in the first Galactic quadrant from the 2.695 GHz Effelsberg survey

A.R. Duncan, P. Reich, W. Reich and E. Fürst

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received 26 May 1999 / Accepted 19 July 1999

Abstract

Polarimetric data from the 2.695 GHz Effelsberg survey of the Galactic Plane have been reduced, resulting in images of the Stokes Q and U emission components over Galactic longitudes given by [FORMULA], at a resolution of [FORMULA]. This extends the earlier work of Junkes et al. (1987a) out to the latitude limit of the survey observations ([FORMULA]). Patchy, diffuse polarised emission is seen to extend to high latitudes ([FORMULA]), with generally brighter polarisation detected above [FORMULA]. The distributions of both the polarised intensities and polarisation position-angles are shown, as a function of Galactic longitude, and compared with similar data from the southern Galactic Plane. These data will assist in higher resolution studies of the Galactic magnetic field and the magneto-ionic properties of the interstellar medium.

Between longitudes of [FORMULA], bright patches of polarised emission are detected, which exhibit quasi-periodic variations of the polarisation angles with scale-sizes of approximately [FORMULA]. Both the characteristics and the possible origins of these structures are discussed. This bright emission appears to originate from the Sagittarius spiral arm, between distances of approximately 2.5 and 8 kpc. An anticorrelation between polarised intensities and regions of enhanced HI gas density (lying at kinematic distances of 2-2.5 kpc) is found. Possible mechanisms are suggested to account for this anticorrelation, arising through the action of a Faraday "screen" associated with the Sagittarius arm.

The structured, quasi-periodic nature of the polarisation position-angles over this region of the Plane most likely results from a peculiar magnetic field geometry associated with the Sagittarius arm. With scale-sizes of between 200 and 600 pc, such magnetic field geometries may be produced by a mechanism similar to the Parker instability.

Key words: techniques: polarimetric – surveys – ISM: magnetic fields – Galaxy: general – radio continuum: general

Send offprint requests to: W. Reich

© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999

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