Turbulence与星系团中由结构形成产生的涡度
Turbulence and Vorticity in Galaxy Clusters Generated by Structure Formation
摘要：
湍流是团内介质演化的关键因素，其性质可以通过高分辨率数值模拟来预测。我们目前的螺线管和压缩湍流的产生在一个小尺寸的集群形成过程中，使用高分辨率，非辐射宇宙学模拟，在一个精细的监测时间在集群内介质的初步结果。在这一系列论文的第一篇中，我们仔细研究了一个模拟的星系团，它的形成是由$z \sim 0.3$周围的合并所区分的。我们分离层流气体运动，湍流和冲击专用的过滤策略和区分螺线管和压缩组件的气体流动使用Hodge-Helmholtz分解。在所有时期，螺线管湍流在中心集群体积中占主导地位的湍流运动（$\sim 95\%$）的耗散。通过压缩模式的耗散被认为是更重要的（$\sim 30 \%$的总数），只有在大半径（$\geq 0.5 ~r_{\rm vir}$）和接近合并事件。我们表明，拟能（涡度平方）是很好的代理螺线管湍流。所有条款统治的涡度拟能的演变（即斜压，压缩，拉伸和平流条款）被发现是显着的，但在金额随时间和地点而变化。在我们的模拟中，涡度拟能的增长有两个重要的趋势：第一，涡度拟能是从外部不断地吸积到星系团中的，并且大部分的吸积涡度拟能是由斜压和压缩过程在外部吸积激波附近产生的。第二，在集群内部涡拉伸是占主导地位的，虽然其他条款也有很大的贡献。
英文摘要：
Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around $z \sim 0.3$. We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge-Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions ($\sim 95\%$) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important ($\sim 30 \%$ of the total) only at large radii ($\geq 0.5 ~r_{\rm vir}$) and close to merger events. We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Second, in the cluster interior vortex stretching is dominant, although the other terms also contribute substantially.
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