Unveiling the nature of radio relics using cosmological simulations and observations

• Applicant: Dr. Sebastian Nuza, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: from 2013 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 247813774

The present project aims at investigating the origin and evolution of radio relics using both observations and cosmological simulations. Since radio relics are believed to be produced during galaxy cluster mergers we plan to simulate a large sample of galaxy clusters up to the present epoch within a large scale cosmological environment. This will permit us to reproduce realistic relic formation scenarios going beyond the simple binary merger situation thus including cosmological substructure. To simulate galaxy clusters at high resolution, we will select cluster candidates from large cosmological boxes in order to (re)simulate them using several numerical schemes (e.g., SPH, VPH, AMR). In this way, we will assess possible differences in the Mach number distributions related to the method adopted to treat the gas hydrodynamics. The latter is important since the diffuse radio emission output is related to the Mach number of the shocked gas, among other thermodynamical quantities. Using physically motivated non-thermal radio emission models we will study the capability of the different scenarios to explain the generation of synchrotron emission under such astrophysical conditions. Since a crucial assumption of these models is the magnetic field value in the shocked gas region we also plan to (re)simulate a sample of galaxy clusters using an MHD approach within the context of SPH. This will let us to consistently evolve the magnetic fields as a function of time including the large scale cosmological environment. We will later combine these magnetic field values with small-scale tangled field models to predict the relic polarization, depolarization and rotation measure properties of every non-thermal scenario to later compare with available observations. Additionally, using this large galaxy cluster sample, we will assess the relevance of merger parameters in the final radio relic luminosity, shock structure, Mach number distribution, etc., as well as the resulting correlations between different observables such as X-ray and radio luminosities in order to shed light on the physical nature of these systems. Furthermore, since in the coming years new radio observatories are expected to produce large relic samples that will need to be interpreted within a theoretical framework, we also plan to use our galaxy cluster sample to compute the radio relic luminosity function in the Universe as a function of merger parameters. In this way, we will be able to infer the statistical properties of the forthcoming large relic samples for a wide variety of observational setups.

• DFG Programme: Research Grants
• International Connection: Spain
• Participating Persons: Privatdozent Dr. Klaus Dolag; Dr. Matthias Hoeft; Professor Dr. Matthias Steinmetz; Professor Dr. Gustavo Yepes