A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN feedback in a low-mass cluster of galaxies

TL;DR

This paper reports on a unique mini radio-halo in a galaxy cluster, featuring giant bubble-like structures likely formed by past AGN activity, providing insights into AGN feedback and cluster dynamics.

Contribution

It presents detailed multi-wavelength observations of an unusual radio source with giant bubbles, revealing a scenario of past AGN activity without current activity, advancing understanding of plasma bubbles in galaxy clusters.

Findings

Giant (~100 kpc) bubble-like radio structures observed without ongoing AGN activity.

Steep radio spectrum indicating radiation losses and buoyant rise of bubbles.

Evidence of particle re-acceleration and AGN-driven energy injection into the cluster medium.

Abstract

We present detailed observations of MRC 0116+111, revealing a luminous, mini radio-halo of ~240 kpc diameter located at the centre of a cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio observations reveal a highly unusual radio source: showing a pair of giant (~100 kpc diameter) bubble-like diffuse structures, that are about three times larger than the analogous extended radio emission observed in M87 - the dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a compact core or active radio jets feeding the plasma bubbles. The radio emitting relativistic particles and magnetic fields were probably seeded in the past by a pair of radio-jets originating in the AGN of the central cD galaxy. The extremely steep high-frequency radio spectrum of the north-western bubble, located ~100 kpc from cluster centre, indicates radiation losses, possibly because having detached, it is rising buoyantly and moving away into the putative hot intra-cluster medium. The other bubble, closer to the cluster centre, shows signs of ongoing particle re-acceleration. We estimate that the radio jets which inflated these two bubbles might have also fed enough energy into the intra-cluster medium to create an enormous system of cavities and shock fronts, and to drive a massive outflow from the AGN, which could counter-balance and even quench a cooling flow. Therefore, this source presents an excellent opportunity to understand the energetics and the dynamical evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.