IUCAA Preprints
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Item Radio observations of ZwCl 2341.1+0000: a double radio relic cluster(2009-10-01) Weeren, R.; Miniati, F.; Bagchi, Joydeep; et al.infall and mergers of smaller subclusters and galaxy groups. Diffuse radio emission, in the form of radio halos and relics, is found in clusters undergoing a merger, indicating that shocks or turbulence associated with the merger are capable of accelerating electrons to highly relativistic energies. Double relics are a rare class of radio sources found in the periphery of clusters, with the two components located symmetrically on the opposite sides of the cluster center. These relics are important probes of the cluster periphery as (i) they provide an estimate of the magnetic field strength, and (ii) together with detailed modeling can be used to derive information about the merger geometry, mass, and timescale. Observations of these double relics can thus be used to test the framework of LSS formation. Here we report on radio observations of ZwCl 2341.1+0000, a complex merging structure of galaxies located at z = 0.27, using Giant Metrewave Radio Telescope (GMRT) observations. Aims. The main aim of the observations is to study the nature of the diffuse radio emission in the galaxy cluster ZwCl 2341.1+0000. Methods. We carried out GMRT 610, 241, and 157 MHz continuum observations of ZwCl 2341.1+0000. The radio observations are combined with X-ray and optical data of the cluster. Results. The GMRT observations show a double peripheral radio relic in the cluster ZwCl 2341.1+0000. The spectral index is −0.49 ± 0.18 for the northern relic and −0.76 ± 0.17 for the southern relic. We have derived values of 0.48 − 0.93 µGauss for the equipartition magnetic field strength. The relics are probably associated with outward traveling merger shock waves.Item Evolution of shocks and turbulence in the formation of galaxy clusters embedded in megaparsec-scale filaments(2011-04-26) Iapichino, L.; Miniati, F.; et al.; Paul, SurajitMassive structures like cluster of galaxies, embedded in cosmic filaments, release enormous amount of energy through their interactions. These events are associated with production of Mpc-scale shocks and injection of considerable amount of turbulence, affecting the non-thermal energy budget of the ICM. In order to study this thoroughly, we performed a set of cosmological simulations using the hydrodynamical code Enzo.We studied the formation of clusters undergoing major mergers, the propagation of merger shocks and their interaction with the filamentary cosmic web. This interaction is shown to pro- duce peripheral structures remarkably similar to giant radio relics observed, for example, in Abell 3376 and Abell 3667. We find a relatively long timescale (about 4 Gyr) for turbulence decay in the centre of major merging clusters. This timescale is substantially longer than typically assumed in the turbulent re-acceleration models, invoked for explaining the statistics of observed radio halos.