Owers, Matt S., Nulsen, Paul E. J., Couch, Warrick J., Ma, Cheng-Jiun, David, Laurence P., Forman, William R., Hopkins, Andrew M., Jones, Christine, and van Weeren, Reinout J. 2014. "A Merger Shock in A2034." The Astrophysical Journal, 780 163. https://doi.org/10.1088/0004-637X/780/2/163.
We present a 250 ks Chandra observation of the cluster merger A2034 with the aim of understanding the nature of a sharp edge previously characterized as a cold front. The new data reveal that the edge is coherent over a larger opening angle and is significantly more bow-shock-shaped than previously thought. Within ~27° about the axis of symmetry of the edge, the density, temperature, and pressure drop abruptly by factors of 1.83^{ 0.09}_{-0.08}, 1.85^{ 0.41}_{-0.41}, and 3.4^{ 0.8}_{-0.7}, respectively. This is inconsistent with the pressure equilibrium expected of a cold front and we conclude that the edge is a shock front. We measure a Mach number M = 1.59^{ 0.06}_{-0.07} and corresponding shock velocity v shock ~= 2057 km s–1. Using spectra collected at the MMT with the Hectospec multi-object spectrograph, we identify 328 spectroscopically confirmed cluster members. Significantly, we find a local peak in the projected galaxy density associated with a bright cluster galaxy that is located just ahead of the nose of the shock. The data are consistent with a merger viewed within ~23° of the plane of the sky. The merging subclusters are now moving apart along a north-south axis approximately 0.3 Gyr after a small impact parameter core passage. The gas core of the secondary subcluster, which was driving the shock, appears to have been disrupted by the merger. Without a driving "piston," we speculate that the shock is dying. Finally, we propose that the diffuse radio emission near the shock is due to the revival of pre-existing radio plasma that has been overrun by the shock.
