Radio continuum observations of the Leo Triplet at 2.64 GHz^⋆

¹ Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków, Poland
e-mail: iwan@oa.uj.edu.pl
² Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ Research Department “Plasmas with Complex Interactions”, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany

Received: 11 January 2013
Accepted: 14 March 2013

Abstract

Context. The Leo Triplet group of galaxies is best known for the impressive bridges of neutral gas that connect its members. One of the bridges forms a large tidal tail extending eastwards from NGC 3628 that hosts several H   i plumes and carries the material from this galaxy to the intergalactic space.

Aims. The magnetic fields of the member galaxies NGC 3628 and NGC 3627 show morphological peculiarities, suggesting that interactions within the group may be caused by stripping of the magnetic field. This process could supply the intergalactic space with magnetised material, a scenario considered as a possible source of intergalactic magnetic fields (as seen eg. in the “Taffy” pairs of galaxies). Additionally, the plumes are likely to be the tidal dwarf galaxy candidates.

Methods. We performed radio continuum mapping observations at 2.64 GHz using the 100-m Effelsberg radio telescope. We obtained total power and polarised intensity maps of the Triplet. These maps were analysed together with the archive data, and the magnetic field strength (as well as the magnetic energy density) was estimated.

Results. Extended emission was not detected either in the total power or the polarised intensity maps. We obtained upper limits of the magnetic field strength and the energy density of the magnetic field in the Triplet. We detected emission from the easternmost clump and determined the strength of its magnetic field. In addition, we measured integrated fluxes of the member galaxies at 2.64 GHz and estimated their total magnetic field strengths.

Conclusions. We found that the tidal tail hosts a tidal dwarf galaxy candidate that possesses a detectable magnetic field with a non-zero ordered component. Extended radio continuum emission, if present, is weaker than the reached confusion limit. The total magnetic field strength does not exceed 2.8 μG and the ordered component is lower than 1.6 μG.