Off-Center Mergers of Clusters of Galaxies and Nonequipartition of Electrons and Ions in the Intracluster Medium
Off-Center Mergers of Clusters of Galaxies and Nonequipartition of Electrons and Ions in the Intracluster Medium
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星系团的偏心合并以及星系团内介质中电子和离子的不均分
DOI：
10.1086/308550
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
M. Takizawa
中科院分区：
文献类型：
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作者：
M. Takizawa
我们研究了星系团的动力学演化及其在偏离中心合并过程中的观测结果，明确考虑了n体和流体动力学模拟中星系团内介质中离子和电子之间的弛豫过程。在收缩阶段，两个子簇之间形成弓形激波。在这个阶段，观测到的两个峰值之间的温度取决于观察角度，即使系统的几何形状看起来非常简单，就像正面碰撞一样。在最收缩的时期，当我们沿着碰撞轴观察合并星团时，它们看起来像具有大温度梯度的球形松弛星团。在膨胀阶段，发生螺旋弓形激波。在正面合并中，电子温度明显低于等离子体平均温度，特别是在膨胀阶段的后激波区域。当系统具有相对较大的角动量时，x射线图像中的双峰结构即使在最收缩期后也能存在。观察角度对x射线图像的形态特征和偏离中心合并的电子温度分布特征都有重要影响。当几乎沿着碰撞轴观察星团时，星系视距（LOS）速度的分布是合并的一个很好的指标。在收缩阶段，对于质量接近相等的碰撞和质量差异较大的碰撞，预期峰态为负，偏度较大。为了获得统计上有意义的结果，大约需要1000个星系的LOS速度。对于附近的星团（z < 0.05），像双度场这样的大型红移调查将使我们能够研究合并动态。
We investigate the dynamical evolution of clusters of galaxies and their observational consequences during off-center mergers, explicitly considering the relaxation process between ions and electrons in the intracluster medium by N-body and hydrodynamical simulations. In the contracting phase, a bow shock is formed between the two subclusters. The observed temperature between two peaks in this phase depends on the viewing angle, even if the geometry of the system seems to be very simple like head-on collisions. Around the most contracting epoch, when we observe merging clusters nearly along the collision axis, they look like spherical relaxed clusters with large temperature gradients. In the expanding phase, spiral bow shocks occur. As in head-on mergers, the electron temperature is significantly lower than the plasma mean one, especially in the postshock regions in the expanding phase. When the systems have relatively large angular momentum, double-peak structures in the X-ray images can survive even after the most contracting epoch. Morphological features in both X-ray images and electron temperature distribution characteristic to off-center mergers are seriously affected by the viewing angle. When the clusters are observed nearly along the collision axis, the distribution of galaxies' line-of-sight (LOS) velocities is a good indicator of mergers. In the contracting phase, a negative kurtosis and a large skewness are expected for nearly equal mass collisions and rather different mass ones, respectively. To obtain statistically significant results, about 1000 galaxies' LOS velocities are required. For nearby clusters (z < 0.05), large redshift surveys such as the Two-Degree Field will enable us to study merger dynamics.