SHOCKS AND CAVITIES FROM MULTIPLE OUTBURSTS IN THE GALAXY GROUP NGC 5813: A WINDOW TO ACTIVE GALACTIC NUCLEUS FEEDBACK
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
- Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22901 (United States)
- Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching (Germany)
- Physics and Astronomy Department, Michigan State University, East Lansing, MI 48824-2320 (United States)
- Institute for Astrophysical Research and Astronomy Department, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)
- KIPAC, Stanford University, 452 Lomita Mall, Stanford, CA 94305 (United States)
We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. The system shows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc from the central source, from three distinct outbursts of the central active galactic nucleus (AGN), which occurred 3 x 10{sup 6}, 2 x 10{sup 7}, and 9 x 10{sup 7} yr ago. The H{alpha} and X-ray observations reveal filaments of cool gas that has been uplifted by the X-ray cavities. The inner two cavity pairs are filled with radio-emitting plasma, and each pair is associated with an elliptical surface brightness edge, which we unambiguously identify as shocks (with measured temperature jumps) with Mach numbers of M {approx} 1.7 and M {approx} 1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise dynamically relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts differs by a factor of six, from (1.5-10)x10{sup 42} erg s{sup -1}, indicating that the mean jet power changes significantly over long ({approx}10{sup 7} yr) timescales. The total energy output of the most recent outburst is also more than an order of magnitude less than the total energy of the previous outburst (1.5 x 10{sup 56} erg versus 4 x 10{sup 57} erg), which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. The outburst interval implied by both the shock and cavity ages ({approx}10{sup 7} yr) indicates that, in this system, shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the intracluster medium and the central supermassive black hole.
- OSTI ID:
- 21567664
- Journal Information:
- Astrophysical Journal, Vol. 726, Issue 2; Other Information: DOI: 10.1088/0004-637X/726/2/86; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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