Speaker
Description
Radio halos are large-scale, diffuse radio sources with low surface brightness located in the central regions of galaxy clusters, extending across several megaparsec scales. They are believed to originate from cosmic rays re-accelerated by merger-induced turbulence by second-order Fermi mechanism. The turbulent re-acceleration model anticipates a substantial population of radio halos with very-steep spectra ($\alpha > 1.5$, where $S_\nu \propto \nu^{-\alpha}$) and a correlation between the turbulent energy, linked to the cluster merger event, and the resulting radio synchrotron spectral shape. But this hypothesis has not been tested extensively due to the absence of low-frequency sensitive radio observations. In this talk, I will present preliminary results on a project aimed to address for the first time in a complete sample the statistical spectral properties of radio halos by combining LOFAR and uGMRT data. The project focuses on a complete sample of 45 radio halos in the Second Data Release of the LOFAR Two-meter Sky Survey (LoTSS-DR2, 150 MHz), which was recently followed up at uGMRT 650 MHz. I will show the first results based on a subsample of 18 radio halos discussing the connection between their spectral properties and the dynamical state of the hosting clusters. Finally I will show how radio halo properties are connected with cluster mass and redshift and discuss implications of my results for the turbulent re-acceleration scenario for the formation of giant radio halos and highlight the importance of this study for future LOFAR observations.
