Cluster mergers and non-thermal phenomena: a statistical magneto-turbulent model
Cluster mergers and non-thermal phenomena: a statistical magneto-turbulent model
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DOI：
10.1111/j.1365-2966.2005.08747.x
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发表时间：
2005-03-11
影响因子：
4.8
通讯作者：
Miniati, F
中科院分区：
文献类型：
--
作者：
Cassano, R;Brunetti, G;Miniati, F
现在有确凿的证据表明，团内介质（ICM）由热等离子体、磁场和相对论粒子的混合物组成。星系团中非热现象的最重要证据来自于在越来越多的大质量星系团中观察到的Mpc尺度上扩散的壮观的同步辐射，以及最近在少数情况下探测到的超过热韧致辐射谱的硬X射线尾。一个很有希望的可能性来解释巨型无线电晕的存在，相对论性电子重新加速的某种湍流产生的集群体积在合并事件。为了研究ICM的热性质和非热性质之间的联系，本文建立了一个统计磁湍流模型，该模型以自洽的方式描述了ICM的热性质和团簇的非热性质的演化。利用扩展的Press-Schechter形式主义，我们遵循集群合并，并估计在这些充满活力的事件中产生的流体湍流的注入率。然后，我们计算的相对论性电子在ICM中的光谱的演化在集群的生活中，考虑到由于合并驱动的湍流和相关的电子的能量损失的电子加速。我们最终与合成人口的星系团的ICM和加速电子发射的非热光谱的演化计算。在模拟的集群中产生的可检测的非热辐射和硬X射线发射被认为是可能的，在主要的合并事件的模型参数的可靠值。此外，无线电晕的发生作为父集群的质量的函数进行计算，并与观测进行比较。在这种情况下，发现模型期望值与观测值非常一致：在我们的合成人口中，大约30%的更大规模的星团中发现了无线电晕（M大于或接近1.8 × 10（15）M-圆点）和大约4%的中等质量星系团（9 × 10（14）< M < 1.8 × 10（15）M-圆点），而射电晕现象在较小的星团中极为罕见。
There is now firm evidence that the intracluster medium (ICM) consists of a mixture of hot plasma, magnetic fields and relativistic particles. The most important evidence for non-thermal phenomena in galaxy clusters comes from the spectacular synchrotron radio emission diffused over Mpc scales observed in a growing number of massive clusters and, more recently, in the hard X-ray tails detected in a few cases in excess of the thermal bremsstrahlung spectrum. A promising possibility to explain giant radio haloes is given by the presence of relativistic electrons reaccelerated by some kind of turbulence generated in the cluster volume during merger events. With the aim of investigating the connection between thermal and non-thermal properties of the ICM, in this paper we develop a statistical magneto-turbulent model which describes in a self-consistent way the evolution of the thermal ICM and that of the non-thermal emission from clusters. Making use of the extended Press-Schechter formalism, we follow cluster mergers and estimate the injection rate of the fluid turbulence generated during these energetic events. We then calculate the evolution of the spectrum of the relativistic electrons in the ICM during the cluster life by taking into account both the electron acceleration due to the merger-driven turbulence and the relevant energy losses of the electrons. We end up with a synthetic population of galaxy clusters for which the evolution of the ICM and of the non-thermal spectrum emitted by the accelerated electrons is calculated. The generation of detectable non-thermal radio and hard X-ray emission in the simulated clusters is found to be possible during major merger events for reliable values of the model parameters. In addition the occurrence of radio haloes as a function of the mass of the parent clusters is calculated and compared with observations. In this case it is found that the model expectations are in good agreement with observations: radio haloes are found in about 30 per cent of the more massive clusters in our synthetic population (M greater than or similar to 1.8 x 10(15) M-circle dot) and in about 4 per cent of the intermediate massive clusters (9 x 10(14) < M < 1.8 x 10(15) M-circle dot), while the radio halo phenomenon is found to be extremely rare in the case of the smaller clusters.