Evidence for Nonhydrostatic Gas Motions in the Hot Interstellar Medium of Centaurus A

• Published in: The Astrophysical journal Vol. 677; no. 2; pp. L97 - L100
• Main Authors: Kraft, R. P, Hardcastle, M. J, Sivakoff, G. R, Jordán, A, Nulsen, P. E. J, Birkinshaw, M, Forman, W. R, Jones, C, Worrall, D. M, Croston, J. H, Evans, D. A, Raychaudhury, S, Murray, S. S, Brassington, N. J, Goodger, J. L, Harris, W. E, Juett, A. M, Sarazin, C. L, Woodley, K. A
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 20-04-2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Jets; X-ray galaxies; galaxies: individual (Centaurus A, NGC 5128)- galaxies: jets-hydrodynamics; X-rays: galaxies; Interstellar matter; Cosmic x-ray sources
• ISSN: 1538-4357; 0004-637X; 1538-4357
• DOI: 10.1086/588023

We present preliminary results from a deep (600 ks) Chandra observation of the hot interstellar medium of the nearby early-type galaxy Centaurus A. We find a surface brightness discontinuity in the gas similar to 3.5 kpc from the nucleus spanning a 120 degree arc. The temperature of the gas is 0.60 plus or minus 0.05 keV (0.68 plus or minus 0.10 keV) Interior (exterior) to the discontinuity. 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 plus or minus 0.4 pressure jump across the discontinuity. This would imply that the gas is moving at 470 plus or minus 100 km s super(-1), or Mach 1.0 plus or minus 0.2 (1.2 plus or minus 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 similar to 7) discontinuity In the elemental abundance. We suggest that the observed discontinuity is the result of nonhydrostatlc 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 after the merger. The pressure discontinuity may have had a profound Influence on the temporal evolution of the kiloparsec-scale jet. The jet could have decollimated, crossing the discontinuity and thereby forming the northeast radio lobe.