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Deciphering RAdio NOn-thermal Emission on the Largest scales

Periodic Reporting for period 3 - DRANOEL (Deciphering RAdio NOn-thermal Emission on the Largest scales)

Reporting period: 2019-10-01 to 2021-03-31

The project DRANOEL aims to understand the origin of the radio emission detected in the most massive objects in our Universe: galaxy clusters. These are the largest gravitationally bounded objects in the Universe, where hundreds to thousands of galaxies co-exist with dark matter, hot and rarefied plasma, and magnetic fields. The intra-cluster medium of galaxy clusters reaches extreme conditions, that are beyond anything achievable in any laboratory on Earth.
A big challenge of modern astrophysics is understanding the origin of radio emission spread over the volume of some galaxy clusters. The emission reaches scales as large as few Megaparsecs and is challenging to explain,
because it requires ultra-relativistic electrons moving around magnetic field lines, but both the origin of the magnetic fields and of the electrons are unknown.
Absolutely fundamental to the understanding of the radio emission in galaxy clusters are a detailed knowledge of the magnetic fields and of the energy spectrum of the emitting particles.
In these years, we are entering into a golden age to address these fundamental problems, thanks to the advent of a new generation of radio telescopes, such as LOFAR, the JVLA, and ASKAP.
At the same time, the new eROSITA X-ray satellite is going to provide us with a wealth of new data on the most distant and less massive galaxy clusters and groups.
DRANOEl has already achieved in the first scientific period fundamental results for the understanding of the non-thermal phenomena in galaxy clusters. Among these, we highlight the discovery of radio emission
in clusters and inter-cluster regions using data from the LOFAR radio telescope, and the first constraints on magnetic field amplification by weak shocks.
From a technological point of view, we are stepping into a new era of observational astronomy: the big-data era. Indeed, large sky surveys are being conducted rather than single pointed observations. This survey era is changing our approach to observational data. It enables to perform all-sky studies but calls for numerical and technological efforts for the data handling.
Along this line, DRANOEL will provide new techniques for the analysis of the data, that will be fundamental for the next generation of radio instruments, such as the Square Kilometer Array (SKA).
During the first period, we already developed new tools that allow one to understand the best way to handle big interferometric data, optimising the size of the datasets and the information that must be recorded.
In addition, new analysis techniques are being implemented for both the analysis of radio polarisation data and low frequency radio data.
These front-line techniques applied to the new data that the project is using, will permit to set milestones in our understanding of radio emission in galaxy clusters.
The open questions that are being addressed by this project are not only important for galaxy clusters, but have a large impact of several inter-connected physical disciplines, such as cosmology, astro-particle physics and plasma physics.
The DRANOEL team is investigating for the first time the low frequency radio emission from galaxy clusters and its connections with radiogalaxies and magnetic fields. This is possible thanks to the developement of innovative techniques for the data reduction and analysis and the usage of cutting edge radio facilities such as the LOw Frequency ARray.
We have discovered several new sources that shine in the intra-cluster medium of galaxy clusters, and obtained the first constraints on the magnetic field morphology at the clusters edge, where gigantic shock waves are propagating.
The results obtained by the team have opened new lines of research, and are providing a new view of the non-thermal phenomena in galaxy clusters.
1) Discovery of new radio emission in galaxy clusters at low radio frequency providing insights on the connection between thermal and non-thermal emission (Bonafede et al 2018)
2) Discovery of the first radio-bridge connecting two galaxu clysrers (Govoni, Orru, Bonafede et al. Science, 2019)
3) Development of new techniques for the optimal usage of LOFAR international stations data (Bonnassieux et al, 2020, MNRAS, in press)
4) First analysis of magnetic field morphology in shocked regions in galaxy clusters and constraints of astrophysical parameters using cosmological simulations (Stuardi et al. 2019)
5) First ever usage of polarisation data from LOFAR to infer magnetic field properties in the outskirts of galaxy clusters (Stuardi et al. 2020, in press)

In the next months, we expect to unveil the role of Active Galactic Nuclei to provide seed particles for radio emission, to constrain the role of magnetic in clusters through cutting-edge polarisation techniques
that we are developing, and to understand the origin of the emission we have discoevered.
Radio, Xray and optical emission from a distant galaxy cluster