Details on the event

01/09/2018

Astrophysics Talk

First study of a small sample of cool-core galaxy clusters at low frequency

Nadia Biava (Unibo - INAF/OAS)

Tuesday 27/04/2021 @ 14:00, Sala IV piano Battiferro

Diffuse radio emission in galaxy clusters is observed with different sizes and properties. Giant halos are Mpc-size radio sources found in merging clusters. They could be powered by re-acceleration of particles by turbulence injected in the intra cluster medium (ICM) during major merger. Mini halos are 100-500 kpc-size radio sources found in clusters with a cool core, i.e. a core characterized by a peaked X-ray surface brightness and a significant drop in temperature at the centre. Mini halos could be either due to re-acceleration of particles by turbulence connected with the sloshing of the cluster core after a minor merger, or to the continuous injection of electrons by inelastic collisions of relativistic cosmic-ray protons with the cluster thermal proton population. Both types of halos are characterized by a steep radio spectrum that makes them brighter at low frequencies. Recent low frequency observations with LOFAR HBA have revealed the unexpected presence of emission on Mpc scales in two clusters that host a cool-core and show no signs of major mergers. These sources suggest that minor mergers – while not sufficiently energetic to disrupt the cool-core - could still trigger particle acceleration in the ICM on scales of hundreds of kpc, generating ultra-steep spectrum emission. To characterize the diffuse radio emission in cool-core galaxy clusters and test the occurrence of the more extended emission recently observed, a sample of eleven clusters with a cool-core and some level of dynamical disturbances, estimated from X-ray observations, was selected and observed with LOFAR at 144 MHz. In this talk, I will present the results we have obtained from LOFAR observations. We found that these sources are rare, only two clusters present diffuse emission beyond the cluster core: A1068 new detection and RXJ 1720.1+2638 already known in literature. We also characterized the spectrum of the emission and compare radio and X-ray observations of the source RXJ 1720.1+2638