A radio continuum study of the Magellanic Clouds. III. The magnetic field in the LMC.
Abstract
Using multi-frequency radio polarization surveys made with the Parkes 64-m telescope, we have investigated the morphology of the magnetic field in the Large Magellanic Cloud (LMC). To this end, a polarization map at λ21 cm has been recently added to the existing data base, rendering possible a polarization study of the LMC at three frequencies. The large-scale structure of the magnetic field in the LMC is derived from the λ12 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 LMC. This symmetry centre of the spiral field is roughly centred at a position ~130 pc from the Kinematical centre. The magnetic field seems to be in the LMC and not part of any pan- Magellanic magnetic field. The most salient polarization structure consists of two large (3-4 kpc) filaments which emerge south and south-west of the giant star- forming complex 30 Dor. The analysis of the observed Faraday rotation and depolarization suggests that the best explanation of the polarization structure is in terms of a giant magnetic loop emerging out 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 anomalous HI component detected recently by Luks & Rohlfs (1992). The most extreme rotation measures appear to be associated with the anomalous HI component. The cause for this observed peculiar structure is as yet unclear, but a relation to the collision between the LMC and the SMC some 4 . 10^8^ yrs ago may not be ruled out.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 1993
- Bibcode:
- 1993A&A...271..402K