Magnetic fields in barred galaxies^*

I. The atlas

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Pushchino Radioastronomy Observatory, Astro Space Center, 142290 Pushchino, Russia & Isaac Newton Institute of Chile, Pushchino Branch
³ XMM-Newton Science Operations Centre, Apdo. 50727, 28080 Madrid, Spain
⁴ Research and Scientific Support Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
⁵ University of Technology Sydney, PO Box 123, Broadway 2007, NSW, Australia
⁶ School of Mathematics and Physics, University of Tasmania, GPO Box 252-21, Hobart, Tas 7001, Australia
⁷ Department of Mathematics, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK
⁸ Department of Physics, Moscow University, 119899 Moscow, Russia

Corresponding author: R. Beck, rbeck@mpifr-bonn.mpg.de

Received: 13 February 2002
Accepted: 29 April 2002

Abstract

The total and polarized radio continuum emission of 20 barred galaxies was observed with the Very Large Array (VLA) at λ3, 6, 18 and 22 cm and with the Australia Telescope Compact Array (ATCA) at λ6 cm and 13 cm. Maps at 30´´ angular resolution are presented here. Polarized emission (and therefore a large-scale regular magnetic field) was detected in 17 galaxies. Most galaxies of our sample are similar to non-barred galaxies with respect to the radio/far-infrared flux correlation and equipartition strength of the total magnetic field. Galaxies with highly elongated bars are not always radio-bright. We discuss the correlation of radio properties with the aspect ratio of the bar and other measures of the bar strength. We introduce a new measure of the bar strength, Λ, related to the quadrupole moment of the bar's gravitational potential. The radio surface brightness I of the barred galaxies in our sample is correlated with Λ, , and thus is highest in galaxies with a long bar where the velocity field is distorted by the bar over a large fraction of the disc. In these galaxies, the pattern of the regular field is significantly different from that in non-barred galaxies. In particular, field enhancements occur upstream of the dust lanes where the field lines are oriented at large angles to the bar's major axis. Polarized radio emission seems to be a good indicator of large-scale non-axisymmetric motions.