Deciphering RAdio NOn-thermal Emission on the Largest scales

Project Information

DRANOEL

Grant agreement ID: 714245

DOI

10.3030/714245

Project closed

EC signature date 18 January 2017

Start date 1 September 2017

End date 31 August 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 496 250,00

EU contribution

€ 1 496 250,00

Coordinated by

ALMA MATER STUDIORUM - UNIVERSITA DI BOLOGNA
Italy

Periodic Reporting for period 5 - DRANOEL (Deciphering RAdio NOn-thermal Emission on the Largest scales)

Reporting period: 2022-10-01 to 2023-08-31

Summary of the context and overall objectives of the project

The goal of DRANOEL is understanding the origin of the radio emission detected in galaxy clusters. Galaxy clusters are massive objects that form at the intersection of large-scale filaments in the cosmic web.
Clusters are formed by subsequent merger of smaller groups and galaxies that are pushed together under the effect of gravity. During these mergers, a huge amount of energy is released in the intra-cluster medium (about 10^64 ergs). Most of this energy is dissipated in the medium heating the gas up to hundreds of millions of degrees Kelvin, through shock waves. A small portion of this energy could be channeled in the acceleration of relativistic electrons and in the amplification of magnetic fields, which would emit synchrotron emission in the radio band.
The big questions that were still open before the project started concerned how this energy could be used to make galaxy clusters shine in the radio band.
Using new radio interefrometers at low ferquecny, such as LOFAR and MeerKAT, tigether with new analysis technique, and coupled with polarization data from VLA< dranoel has set important milestones in the field non galaxy clusters nontehrmal emission.
The objectives of the project, which have successfully been achieved, as described in the Sceintific report, were:
1) Putting the first constraints on magnetic field amplification from shocks;
2) Understanding the link between the different type of radio sources detected in galaxy clusters
3) Constraining the (re)acceleration mechanisms at work in galaxy clusters
To achieve these objetives, the team has developed new tools that allow one handle in the best way big interferometric data, optimising the size of the datasets and the information that must be recorded.
These front-line techniques applied to the new data that the project is using, have allowed us to set milestones in our understanding of radio emission in galaxy clusters, and could be in principle useful for other fields of reserach.
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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The DRANOEL team has investigated for the first time the low frequency radio emission from galaxy clusters and its connections with radiogalaxies and magnetic fields in the intra-cluster medium.
This has been possible thanks to the development of innovative techniques for the data reduction and analysis, and the usage of cutting edge radio facilities such as the LOw Frequency ARray, MeerKAT, MWA, and ASKAP.
The main results achieved by the project are listed below (see also Scientific report for a more detailed explanation)
- Discovery of new radio emission beyond clusters, in the so-called radio bridges, probing that particle acceleration goes beyond clusters. We have also set limits to the presence of radio emission and magnetic fields in intergalactic filaments.
- First constrain of magnetic field amplification in radio relics. We have found that magnetic fields are negligibly amplified by the passage of weak Mach number shocks, and we have discovered that magnetic fields in relics have multiple components, highlighting different shock fronts within the same relic
- We have discovered that relaxed clusters hosting radio min halos can also host large-scale radio emission. This emission could originate from minor mergers and/or off-axis merger which are not energetic enough to disrupt the thermal properties of the cluster core, but that seem to be able to re-accelerate an already existing population of cosmic ray electrons.
- We have published the largest systematic study of galaxy clusters, using data from the LOFAR Two Meter Sky Survey. We have compared the observed properties with existing theoretical model. Despite the general observed properties are in line with model predictions, more complex physics needs to be added to the models to fully explain the results
- We have found the first possible accretion relic ever observed. This diffuse radio emission, located at the outskirts of the Coma cluster, could be the first example of acceleration by accretion shocks.
- We have produced the deepest image of the Coma cluster in radio, hosting the first discovered and best studied radio halo and radio relic. We have been able for the first time, thanks to a combined radio and X-ray analysis, to constrain two important parameters of the turbulent re-acceleration model, finding that the acceleration time can not be constant throughout the cluster, and that the ratio between cosmic ray and thermal energy density must increase with radial distance from the cluster center

The results of the projects have been disseminated to astronomers as well as to the general public, through several press-releases issued by the University of Bologna, often joint with ASTRON (NL), Hambirg University (Germany), INAF (Italy), and CSIRO (Australia)
The results of the project had, are having, and will have an important impact in several astrophysical fields

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

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 galaxy clysrers (Govoni, Orru, Bonafede et al. Science, 2019), and limits to its spectral properties (Pignataro et al 2023)
3) Development of new techniques for the optimal usage of LOFAR international stations data (Bonnassieux et al, 2020, MNRAS)
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, Stuardi et al 2021)
5) First ever usage of polarisation data from LOFAR to infer magnetic field properties in the outskirts of galaxy clusters (Stuardi et al. 2021)
6) Connection between min halos and halos (Biava et al. 2021, Biava et al submitted, Biava et al PhD thesis, Riseley et al 2021, Riseley et al 2022, Riseley et al 2023)
7) Discovery of radio diffuse emission in galaxy groups (Brienza 2021, Nature Astronomy)
8) Discovery of first possible accretion relic in the Coma cluster (Bonafede et al 2022), and constraints on particle acceleration mechanism (Bonafede et al 2021, 2022)
9) The largest sample of radio halos and relics (Botteon et al 2021, Hoang et al 2022)
10) Discovery of emission beyond clusters (Botteon et al 2022, Science)
11) Constraints on magnetic field in intergalactic filaments (Hoang et al 2023)
12) The first connection between AGN shocks and mini halos (Bonafede et al 2023)

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Radio, Xray and optical emission from a distant galaxy cluster