Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging^*

¹ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: mhaverkorn@cfa.harvard.edu
² Leiden Observatory, PO Box 9513, 2300 RA, Leiden, The Netherlands e-mail: katgert@strw.leidenuniv.nl
³ ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands e-mail: ger@astron.nl
⁴ Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 26 May 2003
Accepted: 17 June 2004

Abstract

We describe a first attempt to derive properties of the regular and turbulent Galactic magnetic field from multi-frequency polarimetric observations of the diffuse Galactic synchrotron background. A single-cell-size model of the thin Galactic disk is constructed which includes random and regular magnetic fields and thermal and relativistic electrons. The disk is irradiated from behind with a uniform partially polarized background. Radiation from the background and from the thin disk is Faraday rotated and depolarized while propagating through the medium. The model parameters are estimated from a comparison with 350 MHz observations in two regions at intermediate latitudes done with the Westerbork Synthesis Radio Telescope. We obtain good agreement between the estimates for the random and regular magnetic field strengths and typical scales of structure in the two regions. The regular magnetic field strength found is a few μG, and the ratio of random to regular magnetic field strength  is , for a typical scale of the random component of pc. Furthermore, the regular magnetic field is directed almost perpendicular to the line of sight. This modeling is a potentially powerful method to estimate the structure of the Galactic magnetic field, especially when more polarimetric observations of the diffuse synchrotron background at intermediate latitudes become available.