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低质量SZ选择星系团ACT-CL J0256 .5+0006中的巨大射电晕

A giant radio halo in a low-mass SZ-selected galaxy cluster: ACT-CL J0256.5+0006

Kenda Knowles, Huib T. Intema, Andrew J. Baker, J. Richard Bond, Catherine Cress, Neeraj Gupta, Amir Hajian, Matt Hilton, Adam D. Hincks, Renée Hlozek, Jack P. … 展开作者

Kenda Knowles, Huib T. Intema, Andrew J. Baker, J. Richard Bond, Catherine Cress, Neeraj Gupta, Amir Hajian, Matt Hilton, Adam D. Hincks, Renée Hlozek, Jack P. Hughes, Robert Lindner, Tobias A. Marriage, Felipe Menanteau, Kavilan Moodley, Michael D. Niemack, Erik D. Reese, Jonathan Sievers, Cristóbal Sifón, Raghunathan Srianand, Edward J. Wollack

备注：
Updated version: 21 pages, 17 figures, published in MNRAS
发表信息：
Monthly Notices of the Royal Astronomical Society, 2016, Volume 459, Issue 4, p.4240-4258
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摘要：

利用325 MHz和610 MHz的巨型米波射电望远镜观测了Sunyaev-Zel'dovich（SZ）选择的合并星系团ACT-CL J0256.5+0006（$z = 0.363$）中的巨型射电晕（GRH）。我们发现这个星团有一个微弱的（$S_{610} = 5.6 \pm 1.4$ mJy）射电晕，角范围为2.6弧分，对应于星团红移的0.8 Mpc，使其成为GRH。J 0256是最低质量的系统之一，$M_{\rm 500,SZ} = (5.0 \pm 1.2) \times 10^{14} M_\odot$，发现宿主GRH。我们在325 MHz（$S_{325} = 10.3 \pm 5.3$ mJy）下以较低的显著性测量GRH，获得$α^{610}_{325} = 1.0^{+0.7}_{-0.9}$的光谱指数测量。这一结果与典型射电晕总体的平均光谱指数$α= 1.2 \pm 0.2$一致。采用后一个值，我们确定一个1.4 GHz的无线电功率的$P_{1.4\text{GHz}} = (1.0 \pm 0.3) \times 10^{24}$ W Hz $^{-1}$，把这个集群内的分散已知的缩放关系。各种证据（包括ICM形态）表明ACT-CL J0256.5+0006由两个亚群组成。我们确定合并质量比为7：4，和视线速度差为$v_\perp = 1880 \pm 280$ km s $^{-1}$。我们构建了一个简单的合并模型来推断合并中的相关时间尺度。根据其在$P_{\rm 1.4GHz}{-}L_{\rm X}$标度关系上的位置，我们推断，在第一次岩芯穿越之前，我们观察到ACT-CL J0256.5+0006约5亿年。

英文摘要：

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 MHz and 610 MHz. We find this cluster to host a faint ($S_{610} = 5.6 \pm 1.4$ 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, $M_{\rm 500,SZ} = (5.0 \pm 1.2) \times 10^{14} M_\odot$, found to host a GRH. We measure the GRH at lower significance at 325 MHz ($S_{325} = 10.3 \pm 5.3$ mJy), obtaining a spectral index measurement of $α^{610}_{325} = 1.0^{+0.7}_{-0.9}$. This result is consistent with the mean spectral index of the population of typical radio halos, $α= 1.2 \pm 0.2$. Adopting the latter value, we determine a 1.4 GHz radio power of $P_{1.4\text{GHz}} = (1.0 \pm 0.3) \times 10^{24}$ W Hz$^{-1}$, placing this cluster within the scatter of known scaling relations. Various lines of evidence, including the ICM 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 $v_\perp = 1880 \pm 280$ km s$^{-1}$. We construct a simple merger model to infer relevant time-scales in the merger. From its location on the $P_{\rm 1.4GHz}{-}L_{\rm X}$ scaling relation, we infer that we observe ACT-CL J0256.5+0006 approximately 500 Myr before first core crossing.

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