# Evidence for Non-Hydrostatic Gas Motions in the Hot ISM of Centaurus A - Astrophysics

Abstract: We present preliminary results from a deep 600 ks {\em Chandra} observationof the hot interstellar medium of the nearby early-type galaxy Centaurus A CenA. We find a surface brightness discontinuity in the gas $\sim$3.5 kpc fromthe nucleus spanning a 120$^\circ$ arc. The temperature of the gas is0.60$\pm$0.05 and 0.68$\pm$0.10 keV, interior and exterior to thediscontinuity, respectively. The elemental abundance is poorly constrained bythe spectral fits, but if the abundance is constant across the discontinuity,there is a factor of 2.3$\pm$0.4 pressure jump across the discontinuity. Thiswould imply that the gas is moving at 470$\pm$100 km s$^{-1}$, or Mach1.0$\pm$0.2 1.2$\pm$0.2 relative to the sound speed of the gas externalinternal to the discontinuity. Alternatively, pressure balance could bemaintained if there is a large factor of $\sim$7 discontinuity in theelemental abundance. We suggest that the observed discontinuity is the resultof non-hydrostatic motion of the gas core i.e. sloshing due to the recentmerger. In this situation, both gas motions and abundance gradients areimportant in the visibility of the discontinuity. Cen A is in the late stagesof merging with a small late-type galaxy, and a large discontinuity in densityand abundance across a short distance demonstrates that the gas of the twogalaxies remains poorly mixed even several hundred million years after themerger. The pressure discontinuity may have had a profound influence on thetemporal evolution of the kpc-scale jet. The jet could have decollimatedcrossing the discontinuity and thereby forming the northeast radio lobe.

Author: R. P. Kraft, M. J. Hardcastle, G. R. Sivakoff, A. Jordán, P. E. J. Nulsen, M. Birkinshaw, W. R. Forman, C. Jones, D. M. Worrall,

Source: https://arxiv.org/