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Sausage and Toothbrush clusters: Spectral and morphological signatures of cluster merger shocks

Andra Stroe
Leiden Observatory

Clusters grow by mergers, events which release 10e64 ergs of energy and can produce massive outward-travelling shock waves that can have an important effect on cluster gas and galaxies. Giant radio relics form at these shock fronts, where accelerated electrons emit synchrotron radiation. Despite the great interest in relics, candidates with simple geometry, undisturbed morphology and high surface brightness are scarce. The complex interaction between the merger, the shock wave and gas is likely a fundamental driver of galaxy evolution. The effects of dense environments have been previously investigated for relaxed clusters, but never before in highly disturbed, merging clusters hosting a relic. The sausage and toothbrush clusters are providing us with the unique chance of studying this phenomenon and its effects on the relativistic particles and the cluster galaxies. In order to address many of the unanswered questions, we use a unique combination of facilities (GMRT, WSRT, AMI, INT, LOFAR) to obtain the first cluster-wide, multi-wavelength, multi-method analysis aimed at giving a complete picture of merging clusters hosting relics. We derive physical parameters, such as the Mach number and injection spectral index for the diffuse sources in the field. We present spectral index and curvature maps pinpointing spectral trends conclusive for shock acceleration of relativistic particles and test injection models such as the Jaffe-Perola and Kardashev-Pacholczyk. We present a first 16 GHz, high radio frequency map of a radio relic and find clues that the currently-accepted formation mechanism for relics might be fundamentally flawed. This analysis is fully complemented by an H-alpha mapping of the cluster volume and outskirts. We provide the first direct test whether the shock drives or prohibits star formation to decipher the role of the merger in shaping the Halpha luminosity function. We conclude by presenting the first 60 MHz LOFAR image of this cluster, which enables us to study the spectral index and curvature properties over two orders of magnitude in radio frequency.

2014 April 03, 13:30

Centro de Astrofísica da Universidade do Porto (Classroom)
Rua das Estrelas, 4150-762 Porto

Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia