NGC 4654: polarized radio continuum emission as a diagnostic tool for a galaxy--cluster interaction

Abstract

A recent comparison between deep VLA HI observations and dynamical models of the Virgo cluster spiral galaxy NGC 4654 has shown that only a model involving a combination of a tidal interaction and ram pressure can reproduce the data. Deep radio polarization studies, together with detailed MHD modeling, can independently verify those conclusions, that are based on HI observations and dynamical models. We performed deep polarized radio-continuum observations of the Virgo cluster spiral galaxy NGC 4654 with the Effelsberg 100m telescope at 8.35 GHz and the VLA at 4.85 GHz. Detailed 3D MHD simulations were made to determine the large-scale magnetic field and the emission distribution of the polarized radio continuum in the model, during the galaxy evolution within the cluster environment. This direct comparison between the observed and simulated polarized radio continuum emission corroborates the earlier results, that the galaxy had a recent rapid close encounter with NGC 4639 and is undergoing weak ram pressure by the intracluster medium. This combination of deep radio polarization studies and detailed MHD modeling thus gives us unique insight into the interactions of a galaxy with its cluster environment. It represents a diagnostic tool that is complementary to deep HI observations.