Speaker
Description
LOFAR surveys have enabled unprecedentedly detailed analysis of large-scale, diffuse, and steep-spectrum sources in galaxy clusters, such as radio relics and halos. These are thought to arise from particle re-acceleration operated in the intra-cluster medium (ICM) by shocks and turbulence triggered by a cluster merger. Similar processes are likely also responsible for the re-ignition of fossil electrons from radio galaxies, thus forming amorphous and filamentary sources known as radio phoenices. These are interesting sources to investigate the injection of seed relativistic particles into the ICM, the re-energising mechanisms, and the merging history of the host cluster. However, the ultra-steep spectrum ($\alpha \gtrsim 1.5-2$) of phoenices makes them to be remarkably elusive, and the lack of sensitive and high-resolution multi-wavelength data at low radio frequencies, which are essential for a proper classification, has hampered their study.
LOFAR offers a unique opportunity to investigate phoenices. I will present the analysis of a sample of 7 candidate phoenices, which have been selected by visual inspection of a sample of low-mass and nearby galaxy clusters in LoTSS-DR2, and then followed-up with the uGMRT. I will show radio images, optical/X-ray overlays, and spatially-resolved spectral index maps at 144-400 MHz that we used to confirm the classification of our targets. Our sample highlights the challenges of selection and classification of these sources. I will present the first attempt to derive constraints on the statistical properties of phoenices, by exploring similar correlation to those known for radio relics and halos.
