Speaker
Description
The properties and structure of magnetic fields in the intracluster medium (ICM) and how cosmic rays are distributed/(re)energised are still open questions in the study of galaxy clusters.
Of late, thanks to sensitive low frequency observations, a new type of extended radio emission is being detected in the ICM, known as radio phoenixes.
Unlike other types of diffuse emission associated with galaxy clusters, phoenixes have a very steep spectrum ($\alpha \ge 1.6$) with an irregular morphology. They are thought to trace old plasma originated from formerly active galaxies that has been re-energised by adiabatic compression due to the passage of a shock wave. However, there is no clear evidence that links phoenixes to shocks.
In this talk, I will present spectral analysis of a couple of radio phoenixes performed combining LOFAR LBA and HBA observations with data at higher frequencies, in order to track a possible spectral curvature and estimate the age of cosmic rays.
I will then focus on the sub-arcsec investigation of the filamentary emission of these sources thanks to LOFAR-VLBI. The surface brightness along the filaments doesn’t follow a clear trend, suggesting these regions are uniformly filled with cosmic rays.
On comparing our results with magneto-hydrodynamical simulations of turbulent dynamo operating in the ICM, I will discuss an emerging scenario suggesting that the filamentary emission is likely tracing magnetic fields intrinsic to the ICM.
