THE NONTHERMAL ENERGY CONTENT AND GAMMA-RAY EMISSION OF STARBURST GALAXIES AND CLUSTERS OF GALAXIES

The nonthermal particle production in contemporary starburst galaxies and in galaxy clusters is estimated from the Supernova rate, the iron content, and an evaluation of the dynamical processes which characteri ze these objects. The primary energy derives from SN explosions of mas sive stars. The nonthermal energy is transformed by various secondary processes, like acceleration of particles by Supernova Remnants as wel l as diffusion and/or convection in galactic winds. If convection domi nates, the energy spectrum of nonthermal particles will remain hard. b t greater distances from the galaxy almost the entire enthalpy of ther mal gas and Cosmic Rays will be converted into wind kinetic energy, im plying a fatal adiabatic energy loss for the nonthermal component. If this wind is strong enough then it will end in a strong termination sh ock, producing a new generation of nonthermal particles which are subs equently released without significant adiabatic losses into the extern al medium. In clusters of galaxies this should only be the case for ea rly type galaxies, in agreement with observations. Clusters should als o accumulate their nonthermal component over their entire history and energize it by gravitational contraction. The pion decay gamma-ray flu xes of nearby contemporary starburst galaxies is quite small. However rich clusters should be extended sources of very high energy gamma-ray s, detectable by the next generation of systems of air Cherenkov teles copes. Such observations will provide an independent empirical method to investigate these objects and their cosmological history.