Study of Thermal Instability in Cooling Flow of Hot Intergalactic Gas in Clusters of Galaxies

冷却流动中的热不稳定性主要是用线性理论来研究的。前人的研究指出，星系团的引力场改变了其线性热不稳定性。为了阐明这种对团簇冷却流中质量沉积的影响，需要对非线性阶段的二维或三维热不稳定性进行研究。论文1采用数值流体力学的方法，在简单几何的二维笛卡尔坐标系下研究了集群冷却流中的非线性扰动。我们发现在星系团引力场的作用下，在冷却流的扰动中形成涡旋，并能抑制扰动的热不稳定性。这个现象是我们首先发现的。给出了涡旋形成前扰动冷却的判据。在论文2中，我们采用了较为真实的背景冷却流几何形式，即球面对称流。我们表明，在这种情况下，这些过程实际上发生了涡的形成和扰动的抑制。论文3用数值磁流体力学方法研究了磁场对热不稳定性的影响。研究表明，弱磁场抑制涡旋的形成，在磁场的作用下容易产生热不稳定性。本文提出星系团的物质沉积过程受磁场的调控。

Thermal instability in cooling flows have been studied mainly by linear theory. By previous studies, it is pointed out that gravitational field of cluster of galaxies changes property of linear thermal instability. In order to clarify such effect on the mass deposition in cluster cooling flows, it is needed to study thermal instability in nonlinear stage in 2 or 3 dimension.In paper 1, we study non-linear perturbation in cluster cooling flow in a simple geometry, that is 2-dimension Cartesian coordinate, by using numerical hydrodynamics. We found that vortices are formed in the perturbation in cooling flows by the effect of gravitational field of cluster of galaxies and can suppress thermal instability of the perturbation. This phenomena is first found by us. We give the criterion that the perturbation cools before the vortex is formed.In the paper 2, we have adopted rather real situation for geometry of background cooling flow, that is spherical symmetric flow. We show that the formation of vortices and suppression of perturbations by these process actually occur in this case.In the paper 3, effect of magnetic field on thermal instability is studied by using numerical magneto-hydrodynamics. We have shown weak magnetic field suppress vortex formation and thermal instability is easy to occur by the effect of magnetic field. In this paper, we propose the mass depositon on process is regulated by the magnetic field in cluster of galaxies.