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arXiv 2009.13124astro-ph.HEastro-ph.GA
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合并星系团中的巨Shock Waves(N波)对

Pairs of Giant Shock Waves (N-Waves) in Merging Galaxy Clusters

Congyao Zhang, Eugene Churazov, Irina Zhuravleva

摘要:

当一个子星系团与一个更大的星系团合并时,弓形激波被驱动到子星系团的前面。在后来的合并阶段,这个弓形激波从子星系团中分离出来,成为一个“失控”激波,沿着陡峭的密度梯度向下传播,穿过星系团外围,并大致保持其强度和马赫数。这样的冲击是在星团外围产生射电遗迹的可能候选者。我们认为,在同一个合并阶段,二次冲击形成更接近主集群中心。在通常的流体力学中,与这种结构类似的是N波,其中“N”的尾部是激波非线性演化的结果。在星系团的合并过程中,球形几何和层化可以进一步促进星系团的发展。初级冲击和次级冲击都是单一合并事件的自然结果,而且通常这两个因素都应该存在。然而,在无线电波段,前导激波可能更突出,而拖尾激波可能相反地更容易在X射线中看到。后一个论点意味着,对于X射线数据中发现的一些(尾随)冲击,可能很难识别它们的“伙伴”领先冲击或合并的子集群,这些子集群离集群中心更远。我们认为,后发座星系团和A2744可能是两个例子,在合并后的状态,这种良好的分离激波对。

英文摘要:

When a subcluster merges with a larger galaxy cluster, a bow shock is driven ahead of the subcluster. At a later merger stage, this bow shock separates from the subcluster, becoming a "runaway" shock that propagates down the steep density gradient through the cluster outskirts and approximately maintains its strength and the Mach number. Such shocks are plausible candidates for producing radio relics in the periphery of clusters. We argue that, during the same merger stage, a secondary shock is formed much closer to the main cluster center. A close analog of this structure is known in the usual hydrodynamics as N-waves, where the trailing part of the "N" is the result of the non-linear evolution of a shock. In merging clusters, spherical geometry and stratification could further promote its development. Both the primary and the secondary shocks are the natural outcome of a single merger event and often both components of the pair should be present. However, in the radio band, the leading shock could be more prominent, while the trailing shock might conversely be more easily seen in X-rays. The latter argument implies that for some of the (trailing) shocks found in X-ray data, it might be difficult to identify their "partner" leading shocks or the merging subclusters, which are farther away from the cluster center. We argue that the Coma cluster and A2744 could be two examples in a post-merger state with such well-separated shock pairs.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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