Searching for megahalos in galaxy clusters of the LOFAR Two Meter Sky Survey

Recent low frequency radio observations with the LOFAR interferometer revealed the presence of large scale radio emission in clusters outskirts, which takes the name of megahalo (Cuciti et al. 2022). Megahalos allow us to probe volumes that are 30 times larger than those occupied by radio halos, thus opening the exploration of the large scale structure of the universe in the radio band. The other main characteristic is the almost flat surface brightness on scales of a few hundreds kpc, with values around 10 times lower compared to the average brightness of radio halos. So far, megahalos have been observed in four massive (M>6x10^14 Msun) clusters of the LOFAR Two Meter Sky Survey (LoTSS) and their origin is still unknown. In this work, we analyzed four of the most massive clusters of the LoTSS, which are the best candidates to host large scale emission in the form of megahalos. We detected a megahalo in the galaxy cluster Abell 2219 and derived the upper limits for two clusters in which we did not detect a megahalo with the current sensitivity. We also investigated the position of megahalos in the radio power-mass diagram, finding a hint of increase of luminosity with the cluster mass, although the statistics is still poor.