ar X iv : 0 80 3 . 35 95 v 1 [ as tr o - ph ] 2 5 M ar 2 00 8 Evidence for Non - Hydrostatic Gas Motions in the Hot ISM of Centaurus A

We present preliminary results from a deep (600 ks) Chandra observation of the hot interstellar medium of the nearby early-type galaxy Centaurus A (Cen A). We find a surface brightness discontinuity in the gas ∼3.5 kpc from the nucleus spanning a 120 arc. The temperature of the gas is 0.60±0.05 and 0.68±0.10 keV, interior and exterior to the discontinuity, respectively. The elemental abundance is poorly constrained by the spectral fits, but if the abundance is constant across the discontinuity, there is a factor of 2.3±0.4 pressure jump across the discontinuity. This would imply that the gas is moving at 470±100 km s, or Mach 1.0±0.2 (1.2±0.2) relative to the sound speed of the gas external (internal) to the discontinuity. Alternatively, pressure balance could be maintained if there is a large (factor of ∼7) discontinuity in the elemental abundance. We suggest that the observed discontinuity is the result of non-hydrostatic motion of the gas core (i.e. sloshing) due to the recent merger. In this situation, both gas motions and abundance gradients are important in the visibility of the discontinuity. Cen A is in the late stages of merging with a small late-type galaxy, and a large discontinuity in density and abundance across a short distance demonstrates that the gas of the two galaxies remains poorly mixed even several hundred million years 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 The Ohio State University, Department of Astronomy, 4055 McPherson Laboratory, 140 W. 18th Ave., Columbus, OH 43210 University of Bristol, Department of Physics, Tyndall Avenue, Bristol BS8 ITL, UK University of Birmingham, School of Physics and Astronomy, Edgebaston, Birmingham, B15 2TT, UK McMaster University, Department of Physics and Astronomy, Hamilton, ON L8S 4M1, Canada University of Virginia, Department of Astronomy, P. O. Box 400325, Charlottesville, VA 22904