A RADIO-CONTINUUM STUDY OF THE MAGELLANIC CLOUDS .3. THE MAGNETIC-FIELD IN THE LMC

Using multi-frequency radio polarization surveys made with the Parkes 64-m telescope, we have investigated the morphology of the magnetic fi eld in the Large Magellanic Cloud (LMC). To this end, a polarization m ap at lambda21 cm has been recently added to the existing data base, r endering possible a polarization study of the LMC at three frequencies . The large-scale structure of the magnetic field in the LMC is derive d from the lambda12 cm data under the assumption that Faraday rotation is low at this wavelength. The derived field resembles the pattern of a trailing spiral, in accordance with the sense of rotation of the LM C. This symmetry centre of the spiral field is roughly centred at a po sition approximately 130 pc from the kinematical centre. The magnetic field seems to be in the LMC and not part of any pan-Magellanic magnet ic field. The most salient polarization structure consists of two larg e (3-4 kpc) filaments which emerge south and south-west of the giant s tar-forming complex 30 Dor. The analysis of the observed Faraday rotat ion and depolarization suggests that the best explanation of the polar ization structure is in terms of a giant magnetic loop emerging our of the plane of LMC. This loop, characterized by a high degree of field ordering, is possibly connecting the main disk of the LMC to the anoma lous HI component detected recently by Luks & Rohlfs (1992). The most extreme rotation measures appear to be associated with the anomalous H I component. The cause for this observed peculiar structure is as yet unclear, but a relation to the collision between the LMC and the SMC s ome 4 .10(8) yrs ago may not be ruled out.