A merger shock in A2034

We present a 250ks 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 degrees 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 vshock≃2057 km/s. 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 which is located just ahead of the nose of the shock. The data are consistent with a merger viewed within ∼23 degrees 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 which has been overrun by the shock.