Cluster mergers, core oscillations, and cold fronts

We use numerical simulations with hydrodynamics to demonstrate that a class of cold fronts in galaxy clusters can be attributed to oscillations of the dark matter distribution. The oscillations are initiated by the off-axis passage of a low-mass substructure. From the simulations, we derive three observable morphological features indicative of oscillations: (1) the existence of compressed isophotes, (2) the regions of compression must be alternate (opposite and staggered) and lie on an axis passing through the center of the cluster, and (3) the gradient of each compression region must pass through the center of the cluster. Four of six clusters reported in the literature have cold front morphologies consistent with the presence of oscillations. The clusters with oscillations are A496, A1795, A2142, and RX J1720.1+2638. Galaxy clusters A2256 and A3667 are not consistent, so the cold fronts are interpreted as group remnants. The oscillations may be able to provide sufficient energy to solve the cooling flow problem and, importantly, provide it over an extended duration.