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The bow shock, cold fronts and disintegrating cool core in the merging galaxy group RX J0751.3+5012.

Russell, H.R. and Fabian, A.C. and McNamara, B.R. and Edge, A.C. and Sanders, J.S. and Nulsen, P.E.J. and Baum, S.A. and Donahue, M. and O'Dea, C.P. (2014) 'The bow shock, cold fronts and disintegrating cool core in the merging galaxy group RX J0751.3+5012.', Monthly notices of the Royal Astronomical Society., 444 (1). pp. 629-641.


We present a new Chandra X-ray observation of the off-axis galaxy group merger RX J0751.3+5012. The hot atmospheres of the two colliding groups appear highly distorted by the merger. The images reveal arc-like cold fronts around each group core, produced by the motion through the ambient medium, and the first detection of a group merger shock front. We detect a clear density and temperature jump associated with a bow shock of Mach number M = 1.9 ± 0.4 ahead of the northern group. Using galaxy redshifts and the shock velocity of 1100 ± 300 km s−1, we estimate that the merger axis is only ∼10° from the plane of the sky. From the projected group separation of ∼90 kpc, this corresponds to a time since closest approach of ∼0.1 Gyr. The northern group hosts a dense, cool core with a ram pressure stripped tail of gas extending ∼100 kpc. The sheared sides of this tail appear distorted and broadened by Kelvin–Helmholtz instabilities. We use the presence of this substructure to place an upper limit on the magnetic field strength and, for Spitzer-like viscosity, show that the development of these structures is consistent with the critical perturbation length above which instabilities can grow in the intragroup medium. The northern group core also hosts a galaxy pair, UGC 4052, with a surrounding IR and near-UV ring ∼40 kpc in diameter. The ring may have been produced by tidal stripping of a smaller galaxy by UGC 4052 or it may be a collisional ring generated by a close encounter between the two large galaxies.

Item Type:Article
Keywords:Galaxies: groups: individual: RX J0751.3+5012, Intergalactic medium, X-rays: galaxies: clusters.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:21 July 2014
Date deposited:29 June 2015
Date of first online publication:October 2014
Date first made open access:No date available

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