CHANDRA AND ROSAT OBSERVATIONS OF A194: DETECTION OF AN X-RAY CAVITY AND MAPPING THE DYNAMICS OF THE CLUSTER
- Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22901 (United States)
- Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623 (United States)
- Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-str. 1, 85741 Garching bei Muenchen (Germany)
Based on Chandra and ROSAT observations, we investigated the nearby poor cluster A194, which hosts two luminous radio galaxies, NGC 547 (3C 40B) and NGC 541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r {approx} 34 kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC 547. The estimated age of the cavity is t = 7.9 Multiplication-Sign 10{sup 7} years and the total work of the active galactic nucleus is 3.3 Multiplication-Sign 10{sup 59} erg, hence the cavity power is P{sub cav} = 1.3 Multiplication-Sign 10{sup 44} erg s{sup -1}. Furthermore, in the Chandra images of NGC 545 and NGC 541 we detected sharp surface brightness edges, identified as merger cold fronts, and extended tails. Using the pressure ratios between inside and outside the cold fronts we estimated that the velocities of NGC 545 and NGC 541 correspond to Mach numbers of M = 1.0{sup +0.3}{sub -0.5} and M = 0.9{sup +0.2}{sub -0.5}, respectively. The low radial velocities of these galaxies relative to the mean radial velocity of A194 imply that their motion is oriented approximately in the plane of the sky. Based on these and earlier observations, we concluded that NGC 545 and NGC 541 are falling through the cluster, whose center is NGC 547, suggesting that A194 is undergoing a significant cluster merger event. Additionally, we detected 20 bright X-ray sources around NGC 547 and NGC 541, a surprisingly large number, since the predicted number of resolved low-mass X-ray binaries and cosmic X-ray background sources is 2.2 and 4.1, respectively. To explain the nature of additional sources, different possibilities were considered, none of which are satisfactory. We also studied the origin of X-ray emission in Minkowski's object (MO) and concluded that it is most likely dominated by the population of high-mass X-ray binaries rather than by hot diffuse interstellar medium. Moreover, in view of the galaxy dynamics in A194, we explored the possibility that the starburst in MO was triggered by its past interaction with NGC 541, and concluded that it may be a viable path.
- OSTI ID:
- 22004523
- Journal Information:
- Astrophysical Journal, Vol. 743, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
CHANDRA OBSERVATIONS OF NGC 4342, AN OPTICALLY FAINT, X-RAY GAS-RICH EARLY-TYPE GALAXY
MERGING COLD FRONTS IN THE GALAXY PAIR NGC 7619 AND NGC 7626