The magnetic fields of large Virgo cluster spirals. II^⋆

¹ Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków, Poland
e-mail: mawez@astro.rub.de
² Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 23 January 2012
Accepted: 26 July 2012

Abstract

Context. The Virgo cluster of galaxies provides excellent conditions for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated in detail.

Aims. We extend our systematic search for possible anomalies in the magnetic field structures of Virgo cluster spirals in order to characterize a variety of effects and attribute them to different disturbing agents.

Methods. Six angularly large Virgo cluster spiral galaxies (NGC 4192, NGC 4302, NGC 4303, NGC 4321, NGC 4388, and NGC 4535) were targets of a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz and 8.35 GHz (except for NGC 4388 observed only at 4.85 GHz, and NGC 4535 observed only at 8.35 GHz). The presented two-frequency studies allow Faraday rotation analysis.

Results. Magnetic field structures distorted to various extent are found in all galaxies. Three galaxies (NGC 4302, NGC 4303, and NGC 4321) show some signs of possible tidal interactions, while NGC 4388 and NGC 4535 have very likely experienced strong ram-pressure and shearing effects, respectively, visible as distortions and asymmetries of polarized intensity distributions. As in our previous study, even strongly perturbed galaxies closely follow the radio-far-infrared correlation. In NGC 4303 and NGC 4321, we observe symmetric spiral patterns of the magnetic field and in NGC 4535 an asymmetric pattern.

Conclusions. The cluster environment clearly affects the evolution of its member galaxies via various effects. Magnetic fields allow us to trace even weak interactions that are difficult to detect with other observations. Our results show that the degree of distortions of a galaxy is not a simple function of the distance to the cluster center but reflects also the history of its interactions. The angle Θ between the velocity vector v and the rotation vector Ω of a galaxy may be a general parameter that describes the level of distortions of galactic magnetic fields. Information about the motions of galaxies in the sky plane and their three-dimensional distribution, as well as information about the intracluster medium can also be obtained from the Faraday rotation analysis.