Non-thermal emission from the intracluster medium

An important component of the intracluster medium in galaxy clusters is represented by a population of relativistic electrons, which are detected through their synchrotron diffuse radio emission. I will provide evidence that diffuse radio sources, and thus highly energetic relativistic electrons, can be present within the cluster volume on different scales, at different cluster locations and in clusters with different dynamical conditions. A connection is present between the relativistic and thermal plasma, as demonstrated by the correlation of radio power vs cluster X-ray luminosity (for halos and relics), or vs. cooling flow power (for mini-halos). Models for the origin and the reacceleration of the radio emitting electrons are briefly outlined.