Magnetic fields in barred galaxies

III. The southern peculiar galaxy NGC 2442

¹ University of Technology Sydney, PO Box 123, Broadway 2007, NSW, Australia
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ XMM-Newton Science Operations Centre, European Space Agency, Villafranca, PO Box 50727, 28080 Madrid, Spain
⁴ University of Tasmania, GPO Box 252-21, Hobart 7001, Tasmania, Australia
⁵ Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia

Corresponding author: J. Harnett, jules@eng.uts.edu.au

Received: 23 September 2003
Accepted: 3 April 2004

Abstract

Observations of the southern peculiar galaxy NGC 2442 with the Australia Telescope Compact Array in total and linearly polarized radio continuum at λ6 cm are presented and compared with previously obtained Hα data. The distribution of polarized emission, a signature of regular magnetic fields, reveals some physical phenomena which are unusual among spiral galaxies. We find evidence for tidal interaction and/or ram pressure from the intergalactic medium compressing the magnetic field at the northern and western edges of the galaxy. The radial component of the regular magnetic field in the northern arm is directed away from the centre of the galaxy, a finding which is in contrast to the majority of galaxies studied to date. The oval distortion caused by the interaction generates a sudden jump of the magnetic field pattern upstream of the inner northern spiral arm, similar to galaxies with long bars. An unusual “island” of strong regular magnetic field east of the galaxy is probably the brightest part of a magnetic arm similar to those seen in some normal spiral galaxies, which appear to be phase-shifted images of the preceding optical arm. The strong magnetic field of the “island” may indicate a past phase of active star formation when the preceding optical arm was exposed to ram pressure.