Speaker
Description
Diffuse radio emission has been observed in plenty of galaxy clusters and classified in radio halos, relics or revived fossil plasma depending on its morphological and spectral properties. A category that is still less widely studied is that of radio phoenices. These sources are thought to trace fossil lobes of radio galaxies that have been re-energised by adiabatic compression after the passage of a shock wave. However, their precise origin and connection to shocks is still uncertain.
Radio phoenices are typically characterised by an irregular and filamentary morphology with an ultra-steep radio spectrum ($\alpha\ge1.5-2$). To investigate in more details the radio morphology of these sources we have decided to exploit the low frequency signal and high resolution of LOFAR VLBI data at 144 MHz.
In this talk, I will present for the first time the LOFAR high resolution images of the clusters A1914 and A566.
At sub-arcsecond resolution the emission of the radio phoenix in the cluster A1914 appears composed by two sub-structures, that could be remnant radio lobes. Many filaments have been detected connecting the two components or branching out from them. As the filaments in A1914 are very tangled, we speculate that the filamentary structure becomes more complex with time.
The radio phoenix in the cluster A566 also presents filamentary emission resembling the ``mushroom-shape'' structure observed in M87 (Owen et al. 2000) and in the galaxy group Nest200047 (Brienza et al. 2021).
The detection of filaments within radio sources is becoming frequent thanks to the high resolution and sensitivity observations available nowadays (e.g. Ramatsoku et al. 2020, Rudnick et al. 2022, Brienza et al. 2022). Given the variety of physical conditions in which these structures are observed, their formation should be connected to the dynamics of the magnetized plasma. Inquiring the origin of these filaments could therefore help us to make a step forward on the comprehension of radio phoenices formation.
