LoCuSS：最亮星系团活动、气体冷却和X射线团核动力学扰动之间的联系
LoCuSS: the connection between brightest cluster galaxy activity, gas cooling and dynamical disturbance of X-ray cluster cores
摘要：
我们研究了从本地星团子结构巡天（LoCuSS）中选取的65个X射线星团的星团X射线质心和最亮星团星系（BCG）之间的投影偏移分布，其中值红移为z=0.23。我们发现X射线/BCG投影偏移量和在0.04r500（α）的集群气体密度分布的对数斜率之间存在明显的相关性，这意味着更多的动态扰动集群具有较弱的冷核心。此外，BCG的活动性（H_α和射电辐射）与X射线/BCG偏移量之间存在着密切的对应关系，线发射星系都位于X射线/BCG偏移量<~15 kpc的星系团中。在α < -0.85和偏移< 0.02r500的BCGs中，96%（23/24）具有光学发射，88%（21/24）具有放射活性，而没有一个具有超出这些标准的光学发射。我们还研究了r500内的团簇气体分数（fgas），并发现与X射线/BCG投影偏移量的显着相关性。“小偏移量”星系团（<0.02 r500）的平均fgas为0.106+/-0.005（sigma=0.03），而偏移量> 0.02 r500的星系团为0.145+/-0.009（sigma=0.04），这表明在具有较大X射线/BCG偏移量的星系团中，总质量可能被系统性地低估。我们的研究结果意味着冷芯强度和集群动力学状态之间的联系一致的观点，集群合并可以显着扰动冷芯，并设置新的约束模型的集群内介质的演变。
英文摘要：
We study the distribution of projected offsets between the cluster X-ray centroid and the brightest cluster galaxy (BCG) for 65 X-ray selected clusters from the Local Cluster Substructure Survey (LoCuSS), with a median redshift of z=0.23. We find a clear correlation between X-ray/BCG projected offset and the logarithmic slope of the cluster gas density profile at 0.04r500 (alpha), implying that more dynamically disturbed clusters have weaker cool cores. Furthermore, there is a close correspondence between the activity of the BCG, in terms of detected H_alpha and radio emission, and the X-ray/BCG offset, with the line emitting galaxies all residing in clusters with X-ray/BCG offsets of <~15 kpc. Of the BCGs with alpha < -0.85 and an offset < 0.02r500, 96 per cent (23/24) have optical emission and 88 per cent (21/24) are radio active, while none has optical emission outside these criteria. We also study the cluster gas fraction (fgas) within r500 and find a significant correlation with X-ray/BCG projected offset. The mean fgas of the `small offset' clusters (< 0.02r500) is 0.106+/-0.005 (sigma=0.03) compared to 0.145+/-0.009 (sigma=0.04) for those with an offset > 0.02r500, indicating that the total mass may be systematically underestimated in clusters with larger X-ray/BCG offsets. Our results imply a link between cool core strength and cluster dynamical state consistent with the view that cluster mergers can significantly perturb cool cores, and set new constraints on models of the evolution of the intracluster medium.
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