A morphological comparison between giant radio halos and radio mini–halos in galaxy clusters

In this letter we present a morphological comparison between giant radio halos and radio mini-halos in galaxy clusters based on radio–X-ray luminosity, P1.4-LX, and radio luminosity-size, P1.4-RH, correlations. We report evidence that P1.4-LX and P1.4-RH trends may also exist for mini–halos: mini–halo clusters share the same region of giant halo clusters in the (P1.4, LX) plane, whereas they are clearly separated in the (P1.4,RH) plane. The synchrotron emissivity of mini-halos is found to be more than 50 times larger than that of giant halos, implying a very efficient process for their origins. By assuming a scenario of sporadical turbulent particle re-acceleration for both giant and mini halos, we discuss basic physical differences between these sources. Regardless of the origin of the turbulence, a more efficient source of injection of particles, which eventually takes part in the re-acceleration process, is required in mini-halos, and this may result from the central radio galaxy or from proton-proton collisions in the dense cool core regions.