Abstract
The Shapley Concentration (SC) is a galaxy supercluster (few tens of degrees) in the Local Universe (<z>∼0.048) which is currently undergoing cluster mergers and group accretion. It is a diversified environment, with cluster complexes in advanced evolutionary stage, groups of clusters in the very early stages of merger, fairly massive clusters with ongoing accretion activity, and smaller groups located in filaments. These features make the SC an ideal place to observe the signatures of the formation of large-scale structures in the Universe. As a matter of fact, the SC has been observed over a broad range of frequencies with the most important observatories, allowing for a unique multiband study. In this paper, we will present new results from an ongoing study of the Shapley Concentration Core, which is being carried out with the Giant Metrewave Radio Telescope (GMRT). Our work confirms the role played by radio observations in disentangling the details of the accretion and merging processes, and delivers a wealth of information in regions well outside the cluster cores. In particular, we will report on the discovery of a relic in the region between the two clusters A 3558 and A 3562, and of the radio properties of the brightest galaxy in the peripheral cluster A 3556.
Highlights
Universe (∼0.048) which is currently undergoing cluster mergers and group accretion
According to the hierarchical scenario, cluster mergers—the most energetic events in the Universe, with a total energy output of the order of 1063 –1064 erg—are the natural way to account for mass assembly: galaxy clusters form as a consequence of merger trees, to reach and exceed masses on the order of 1015 MSun
Cluster mergers deeply affect the dynamics of the galaxies, as well as the properties of the thermal intracluster medium and those of relativistic particles and magnetic field
Summary
According to the hierarchical scenario, cluster mergers—the most energetic events in the Universe, with a total energy output of the order of 1063 –1064 erg—are the natural way to account for mass assembly: galaxy clusters form as a consequence of merger trees, to reach and exceed masses on the order of 1015 MSun. (4) giant radio halos with ultrasteep spectrum (α ≥ 1.5 − 1.6 for S∝ ν−α ) have been found by means of deep observations at frequencies below 1 GHz (some remarkable examples are A 521, Brunetti et al [8] and Dallacasa et al [9]; A 697, Macario et al [10]; RXCJ 1514.9-1523, Giacintucci et al [11]) Such class of diffuse cluster sources is predicted by the re-acceleration model in the presence of minor mergers; i.e., less energetic and/or less massive (5 − 8 × 1014 MSun ) merger events (Cassano [12]);. Gitti et al [26])
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