Merger shocks in galaxy clusters A665 and A2163 and their relation to radio halos

We present Chandra gas temperature maps for two hot, intermediate-redshift clusters, A665 and A2163. Both show strong temperature variations in their central r = 0.5 h(-1) Mpc regions, naturally interpreted as products of the subcluster mergers. The A665 map reveals a shock in front of the cool core, while the temperature structure of A2163 is more complicated. On a larger linear scale, our data on A2163 indicate a radial temperature decline in agreement with earlier ASCA results, although the uncertainties are large. Both these clusters exhibit previously known synchrotron radio halos. Comparison of the radio images and the gas temperature maps indicates that radio emission predominantly comes from the hot gas regions, providing a strong argument in favor of the hypothesis that relativistic electrons are accelerated in merger shocks.