The generation of optical emission-line filaments in galaxy clusters
Edward Pope, Julian Pittard, Thomas Hartquist, Sam Falle
备注：
15 pages, 18 figures. Altered density values in table 1, which were a factor of 1000 too small. Also extended caption for table 1 to show the mass outflow rate. Accepted for publication in MNRAS
Recent data support the idea that the filaments observed in H_alpha emission near the centres of some galaxy clusters were shaped by bulk flows within their intracluster media. We present numerical simulations of evaporated clump material interacting with impinging winds to investigate this possibility. In each simulation, a clump falls due to gravity while the drag of a wind retards the fall of evaporated material leading to elongation of the tail. However, we find that long filaments can only form if the outflowing wind velocity is sufficiently large, 10^8 cm s^-1. Otherwise, the tail material sinks almost as quickly as the cloud. For reasonable values of parameters, the morphological structure of a tail is qualitatively similar to those observed in clusters. Under certain conditions, the kinematics of the tail resemble those reported in Hatch et al.(2006). A comparison of the observations with the numerical results indicates that the filaments are likely to be a few tens of Myrs old. We also present arguments which suggest that the momentum transfer, from an outflowing wind, in the formation of these filaments is probably significant. As a result, tail formation could play a role in dissipating some of the energy injected by a central AGN close to the cluster centre where it is needed most. The trapping of energy by the cold gas may provide an additional feedback mechanism that helps to regulate the heating of the central regions of galaxy clusters and couple the AGN to the ICM.
The relationship between the optical Halpha filaments and the X-ray emission in the core of the Perseus cluster
NGC 1275位于英仙座星系团Abell 426的中心，被一个壮观的球状阿尔法星云所包围。深钱德拉X射线成像显示，在软X射线中也可以检测到更亮的外部细丝。这可能是由于暗条中的冷气体与热的、致密的团内介质的传导和混合。我们在两个波段的灯丝的对应关系，并提请注意的关系，两个突出的弯曲的西北灯丝的外部，浮力无线电泡被视为一个洞的X射线图像。在孔的形状和细丝的分布上，与水中上升的大气泡的行为非常相似。如果这是一个正确的类比，那么流动是层流，而这个射电源周围的星团内气体不是湍流。我们得到了这种气体粘度的一个极限。
