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|Title:||The two-component giant radio halo in the galaxy cluster Abell 2142||Authors:||VENTURI, Tiziana
Lal, D. V.
Shimwell, T. W.
|Issue Date:||2017||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||603||First Page:||A125||Abstract:||Aims: We report on a spectral study at radio frequencies of the giant radio halo in A 2142 (z = 0.0909), which we performed to explore its nature and origin. The optical and X-ray properties of the cluster suggest that A 2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. Methods: We performed deep radio observations of A 2142 with the Giant Metrewave Radio Telescope (GMRT) at 608 MHz, 322 MHz, and 234 MHz and with the Very Large Array (VLA) in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions, from the galaxy scale, I.e. 5'', up to 60'' to image the diffuse cluster-scale emission. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A 2142, about 1 Mpc away from the cluster centre. We studied the spectral index in two regions: the central part of the halo, where the X-ray emission peaks and the two brightest dominant galaxies are located; and a second region, known as the ridge (in the direction of the most distant south-eastern cold front), selected to follow the bright part of the halo and X-ray emission. We complemented our deep observations with a preliminary LOw Frequency ARray (LOFAR) image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. <BR /> Results: The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, I.e. α<SUP>1.78 GHz</SUP><SUB>118 MHz</SUB> = 1.33 ± 0.08 . The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, I.e. α<SUP>1.78 GHz</SUP><SUB>118 MHz</SUB> 1.5. We propose that the brightest part of the radio halo is powered by the central sloshing in A 2142, in a process similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On the other hand, the steeper ridge may probe particle re-acceleration by turbulence generated either by stirring the gas and magnetic fields on a larger scale or by less energetic mechanisms, such as continuous infall of galaxy groups or an off-axis (minor) merger.||URI:||http://hdl.handle.net/20.500.12386/27346||URL:||https://www.aanda.org/articles/aa/abs/2017/07/aa30014-16/aa30014-16.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201630014||Bibcode ADS:||2017A&A...603A.125V||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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