Publication Date:
2016-05-22
Description:
We present the detection of a giant radio halo (GRH) in the Sunyaev–Zel'dovich (SZ)-selected merging galaxy cluster ACT-CL J0256.5+0006 ( z = 0.363), observed with the Giant Metrewave Radio Telescope at 325 and 610 MHz. We find this cluster to host a faint ( S 610 = 5.6 ± 1.4 mJy) radio halo with an angular extent of 2.6 arcmin, corresponding to 0.8 Mpc at the cluster redshift, qualifying it as a GRH. J0256 is one of the lowest mass systems, M 500, SZ = (5.0 ± 1.2) x 10 14 M , found to host a GRH. We measure the GRH at lower significance at 325 MHz ( S 325 = 10.3 ± 5.3 mJy), obtaining a spectral index measurement of $\alpha ^{610}_{325} = 1.0^{+0.7}_{-0.9}$ . This result is consistent with the mean spectral index of the population of typical radio haloes, α = 1.2 ± 0.2. Adopting the latter value, we determine a 1.4 GHz radio power of P 1.4 GHz = (1.0 ± 0.3) x 10 24 W Hz –1 , placing this cluster within the scatter of known scaling relations. Various lines of evidence, including the intracluster medium morphology, suggest that ACT-CL J0256.5+0006 is composed of two subclusters. We determine a merger mass ratio of 7:4, and a line-of-sight velocity difference of v = 1880 ± 210 km s –1 . We construct a simple merger model to infer relevant time-scales in the merger. From its location on the P 1.4 GHz – L X scaling relation, we infer that we observe ACT-CL J0256.5+0006 just before first core crossing.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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