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

TL;DR

This study compares the morphology of giant radio halos and mini-halos in galaxy clusters, revealing differences in their luminosity-size relations and synchrotron emissivity, and discusses their potential physical origins.

Contribution

It provides the first detailed morphological comparison between giant and mini radio halos using radio-X-ray correlations and highlights key differences in their physical properties.

Findings

Mini-halos share the same P_{1.4}-L_X region as giant halos.

Mini-halos have over 50 times higher synchrotron emissivity.

Different physical mechanisms may drive the origin of mini-halos.

Abstract

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, P_{1.4}-L_X, and radio luminosity-size, P_{1.4}-R_H, correlations. We report evidence that P_{1.4}-L_X and P_{1.4}-R_H trends may also exist for mini--halos: mini--halo clusters share the same region of giant halo clusters in the (P_{1.4},L_X) plane, whereas they are clearly separated in the (P_{1.4},R_H) 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.