Speaker
Description
Radio halos are diffuse, large-scale radio sources with low surface brightness situated in the central region of galaxy clusters, extending over megaparsec scales. They are believed to originate from cosmic rays re-accelerated by merger-driven 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. However, this hypothesis has not been extensively tested due to limited sensitive low-frequency radio observations. In this talk, I will present the first statistical analysis of the spectral properties of radio halos using a complete sample 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 (Band04, 650 MHz). In this talk, the first results will be highlighted based on a fully analyzed subsample of 30 radio halos, discussing the connection between their spectral properties and the dynamical state of the hosting clusters. Finally, I will explore how radio halo properties depend on cluster mass and redshift, discuss the implications for the turbulent re-acceleration model, and emphasize the relevance of these findings for future observations with the SKA. These findings lay the groundwork for interpreting the much larger and more diverse samples expected from future SKA surveys, which will significantly enhance our understanding of the origin of radio halos.
| Topics | Galaxy Clusters & LSS (relativistic particles and magnetic fields) |
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