A dynamical model for the heavily ram pressure stripped Virgo spiral galaxy NGC 4522

¹ CDS, Observatoire astronomique de Strasbourg, 11 rue de l'université, 67000 Strasbourg, France e-mail: bvollmer@astro.u-strasbg.fr
² Astronomical Observatory, Jagiellonian University, Kraków, Poland
³ Yale University Astronomy Department, PO Box 208101, New Haven, CT 06520-8101, USA
⁴ Department of Astronomy, Columbia University, 538 West 120th Street, New York, NY 10027, USA
⁵ Max-Planck-Insitut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 2 February 2006
Accepted: 27 March 2006

Abstract

Context.Recent Hi and Hα observations of NGC 4522 have revealed that this spiral galaxy represents one of the best cases of ongoing ram pressure stripping in the Virgo cluster.

Aims.We determined the parameters of the interaction between the interstellar medium of NGC 4522 and the intracluster medium of the Virgo cluster.

Methods.A dynamical model including ram pressure stripping is applied to the strongly Hi deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is compared with existing VLA Hi observations.

Results.The model successfully reproduces the large-scale gas distribution and the velocity field. However it fails to reproduce the large observed Hi linewidths in the extraplanar component, for which we give possible explanations. In a second step, we solve the induction equation on the velocity fields of the dynamical model and calculate the large scale magnetic field. Assuming a Gaussian distribution of relativistic electrons we obtain the distribution of polarized radio continuum emission which is also compared with our VLA observations at 6 cm. The observed maximum of the polarized radio continuum emission is successfully reproduced. Our model suggests that the ram pressure maximum occurred only ∼50 Myr ago.

Conclusions.Since NGC 4522 is located far away from the cluster center (∼1 Mpc) where the intracluster medium density is too low to cause the observed stripping if the intracluster medium is static and smooth, two scenarios are envisaged: (i) the galaxy moves very rapidly within the intracluster medium and is not even bound to the cluster; in this case the galaxy has just passed the region of highest intracluster medium density; (ii) the intracluster medium is not static but moving due to the infall of the M 49 group of galaxies. In this case the galaxy has just passed the region of highest intracluster medium velocity. This study shows the strength of combining high resolution Hi and polarized radio continuum emission with detailed numerical modeling of the evolution of the gas and the large-scale magnetic field.