The Gas Dynamics of NGC 4472 Revealed by XMM-Newton

We present results from a 100 ks XMM-Newton observation of the hot gas in the Virgo cluster elliptical galaxy NGC 4472. We find a surface brightness discontinuity ∼21 kpc north of the nucleus, consistent with being a contact discontinuity between two moving fluids. We also detect a >60 kpc long ram-pressure stripped tail. The pressure across the discontinuity implies an infall velocity, vinfall, of 1000 km s < vinfall <2200 km s −1 depending on what assumptions are made about the density and pressure of the external gas. We suggest that the NGC 4472 group is falling into a collapsing filament, which is itself falling into the Virgo cluster. The gas of a collapsing filament is rapidly decelerated as it crosses the standoff shock, but the apparent high velocity of infall of NGC 4472 could be simply due to the fact that the gravitating potential of the NGC 4472 group is unaffected by this shock. The group will fall through the shock its gas will be stripped as it passed through the stalled gas of the filament. Additionally, we find two sets of cool filamentary arms to the east and the southwest of the nucleus. One of the southwest arms is co-incident with a sharp filament seen with Chandra. We interpret these arms as filaments of cool gas that have been driven out from the center of the galaxy by the buoyant evolution of a radio bubble. The age of this outburst is ∼10 yrs assuming that the buoyant bubble rises with a velocity of ∼0.4cs=200 km s −1 and the energy of the outburst is a modest ∼2×10 ergs. Subject headings: galaxies: individual (NGC 4472) X-rays: galaxies hydrodynamics galaxies: jets Harvard/Smithsonian Center for Astrophysics, 60 Garden St., MS-67, Cambridge, MA 02138 University of Hertfordshire, School of Physics, Astronomy, and Mathematics, Hatfield AL10 9AB, UK University of Birmingham, School of Physics and Astronomy, Edgebaston, Birmingham, B15, 2TT, UK MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Ave., Cambridge, MA 02139, USA University of Virginia, Department of Astronomy, Charlottesville, VA 22904, USA