Creation of X‐Ray Cavities in Galaxy Clusters with Cosmic Rays

We describe how AGN-produced cosmic rays form large X-ray cavities and radiolobes in the hot diffuse gas in galaxy groups and clusters. Cosmic rays areassumed to be produced in a small shocked region near the cavity center, suchas at the working surface of a radio jet. The coupled equations for gasdynamicsand cosmic ray diffusion are solved with various assumptions about thediffusion coefficient. To form large, long-lived cavities similar to thoseobserved, the diffusion coefficient must not exceed kappa = 10^28 cm^2/s in thehot gas, very similar to values required in models of cosmic ray diffusion inthe Milky Way. When kappa does not exceed 10^28, cosmic rays are confinedwithin the cavities for times comparable to the cavity buoyancy time, asimplied by observations of X-ray cavities and their radio synchrotron emission.Collisions of proton cosmic rays with thermal plasma nuclei followed by piondecay can result in enhanced gamma ray emission from the cavity walls.Comment: 16 pages, 10 figures, accepted by Ap