Ram pressure stripping and the formation of cold fronts
Ram pressure stripping and the formation of cold fronts
复制标题
冲压压力剥离和冷锋的形成
DOI：
10.1046/j.1365-2966.2003.07066.x
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发表时间：
2003
影响因子：
4.8
通讯作者：
U. Briel
中科院分区：
文献类型：
--
作者：
S. Heinz;E. Churazov;W. Forman;C. Jones;U. Briel
钱德拉和xmm -牛顿对许多星团的观测揭示了表面亮度的明显不连续性，与激波不同的是，在不连续性的x射线较亮的一侧，气体温度较低。因此，这些特征被称为“冷锋”。一些冷锋是在子星系团与另一个星系团合并时形成的，而在子星系团外流动的气体的冲击压力使接触不连续呈现出特有的弯曲形状。正如Dupke & White在A496的案例中提出的那样，一些边缘可能不是直接由合并产生的，但本文关注的是合并子星团与周围星团气体之间的接触不连续。我们认为，经过合并子星团的气体流在云团内部引起了缓慢的运动。这些运动将气体从亚星团的中心部分输送到界面。因为在一个典型的团簇或群中（即使是等温的），中心区域的气体熵明显低于外部区域，低熵气体向界面的传输和相关的绝热膨胀使得界面内的气体温度立即低于系统中任何其他地方，从而增强了界面上的温度跳跃，使接触不连续的“尖端”变冷。我们用xmm -牛顿的A3667星团气体温度图来说明这张图。
Chandra and XMM–Newton observations of many clusters reveal sharp discontinuities in the surface brightness, which, unlike shocks, have lower gas temperature on the X-ray brighter side of the discontinuity. For this reason, these features are called ‘cold fronts’. It is believed that some cold fronts are formed when a subcluster merges with another cluster and the ram pressure of gas flowing outside the subcluster gives the contact discontinuity the characteristic curved shape. While some edges may not arise directly from mergers, as was argued by Dupke & White for the case of A496, this paper focuses on those which arise as contact discontinuities between a merging subcluster and the ambient cluster gas. We argue that the flow of gas past the merging subcluster induces slow motions inside the cloud. These motions transport gas from the central parts of the subcluster towards the interface. Because in a typical cluster or group (even an isothermal one) the entropy of the gas in the central regions is significantly lower than in the outer regions, the transport of the low entropy gas towards the interface and the associated adiabatic expansion makes the gas temperature immediately inside the interface lower than in any other place in the system, thus enhancing the temperature jump across the interface and making the ‘tip’ of the contact discontinuity cool. We illustrate this picture with the XMM–Newton gas temperature map of the A3667 cluster.