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The Extended GMRT Radio Halo Survey - I. New upper limits on radio halos and mini-halos

2013; EDP Sciences; Volume: 557; Issue: 557 Linguagem: Inglês

1432-0746

Ruta Kale, T. Venturi, S. Giacintucci, D. Dallacasa, R. Cassano, G. Brunetti, G. Macario, R. Athreya,

Astrophysical Phenomena and Observations

Context. A fraction of galaxy clusters host diffuse radio sources called radio halos, radio relics and mini- halos. These are associated with the relativistic electrons and magnetic fields present over∼ Mpc scales in the intra-cluster medium. Aims. We aim to carry out a systematic radio survey of all luminous galaxy clusters selected from the REFLEX and eBCS X-ray catalogs with the Giant Metrewave Radio Telescope, to understand the statistical properties of the diffuse radio emission in galaxy clusters. Methods. We present the sample and first results from the Extended GMRT Radio Halo Survey (EGRHS), which is an extension of the GMRT Radio Halo Survey (GRHS, Venturi et al. 2007, 2008). Results. Analysis of radio data at 610/ 235/ 325 MHz on 12 galaxy clusters are presented. We report the detection of a newly discovered mini-halo in the cluster RXJ1532.9+3021 at 610 MHz. The presence of a small scale relic (∼ 200 kpc) is suspected in the cluster Z348. We do not detect cluster-scale diffuse emission in 11 clusters. Robust upper limits on the detection of radio halo of size of 1 Mpc are determined. We also present upper limits on the detections of mini-halos in a sub-sample of cool-core clusters. The upper limits for radio halos and mini-halos are plotted in th e radio power- X-ray luminosity plane and the correlations are discussed. Diffuse extended emission, not related to the target clusters, b ut detected as by-products in the sensitive images of two of the cluster fields (A689 and RXJ0439.0+0715) are reported. Conclusions. Based on the information about the presence of radio halos (or upper limits), available on 48 clusters out of the total sample of 67 clusters (EGRHS+GRHS), we find that 23±7% of the clusters host radio halos. The radio halo fraction rises to 31±11%, when only the clusters with X-ray luminosities > 8× 10 44 erg s −1 are considered. Mini-halos are found in∼ 50% of cool-core clusters. A qualitative examination of the X-ray images of the clusters with no diffuse radio emission indicates that a majority of these cluste rs do not show extreme dynamical disturbances and supports the idea that mergers play an important role in the generation of radio halos/relics. The analysis of the full sample will be presented in a future work.