Hot gas in Mach cones around Virgo cluster spiral galaxies⋆
Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
2 CDS, Observatoire astronomique de Strasbourg, UMR7550, 11 rue de l’université, 67000 Strasbourg, France
3 ESAC, XMM-Newton Science Operations Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
4 Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków, Poland
Received: 17 December 2010
Accepted: 8 April 2011
Context. The detailed comparison between observations and simulations of ram-pressure stripped spiral galaxies in the Virgo cluster has led to a 3D view of the galaxy orbits within the hot intracluster medium. The 3D velocities and Mach numbers derived from simulations can be used to derive simple Mach cone geometries for Virgo spiral galaxies.
Aims. We search for indications of hot gas within Mach cones in X-ray observations of selected Virgo cluster spiral galaxies (NGC 4569, NGC 4388, and NGC 4501).
Methods. Low-resolution maps of diffuse extended emission and X-ray spectra from XMM-Newton observations are presented. Gas densities and temperatures were derived from the X-ray spectra.
Results. We find extraplanar diffuse X-ray emission in all galaxies. Based on the 3D velocity vectors from dynamical modeling, a simple Mach cone is fitted to the triangular shape of NGC 4569’s diffuse X-ray emission. Assuming that all extraplanar diffuse X-ray emission has to be located inside the Mach cone, we also fit Mach cones to NGC 4388’s and NGC 4501’s extraplanar X-ray emission. For NGC 4569 it is hard to reconcile the derived Mach cone opening angle with a Mach number based on the sound speed alone. Instead, a Mach number involving the Alfvénic speed seems to be more appropriate, yielding a magnetic field strength of ~1–3 μG for an intracluster medium density of n ~ 10-4 cm-3. Whereas the temperature of the hot component of NGC 4569’s X-ray halo (0.5 keV) is at the high end, but typical of a galactic outflow, the temperature of the hot gas tails of NGC 4388 and NGC 4501 are significantly hotter (0.7–0.9 keV).
Conclusions. In NGC 4569 we find direct evidence of a Mach cone that is filled with hot gas from a galactic superwind. We suggest that the high gas temperatures in the X-ray tails of NGC 4388 and NGC 4501 come from the mixing of the stripped ISM into the hot intracluster medium of the Virgo cluster.
Key words: galaxies: clusters: general / galaxies: clusters: individual: Virgo / galaxies: individual: NGC 4388 / galaxies: individual: NGC 4501 / galaxies: individual: NGC 4569 / galaxies: clusters: intracluster medium
© ESO, 2011