Nonhydrostatic Gas in the Core of the Relaxed Galaxy Cluster A1795
Nonhydrostatic Gas in the Core of the Relaxed Galaxy Cluster A1795
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DOI：
10.1086/337973
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发表时间：
2001-08
期刊：
影响因子：
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通讯作者：
M. Markevitch;M. Markevitch;Alexey Vikhlinin;A. Vikhlinin;P. Mazzotta
中科院分区：
文献类型：
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作者：
M. Markevitch;M. Markevitch;Alexey Vikhlinin;A. Vikhlinin;P. Mazzotta
A1795上的Chandra数据显示，在r=60h-1kpc时，星系团南区的气体密度和温度有轻微的边缘状不连续。边缘内部的气体密度是外部的1.3-1.5倍，温度是外部的1.3-1.5倍，而压力是连续的，这表明这是一个冷锋，两个移动的气体之间的接触面。压力的连续性表明气体的当前相对速度接近于零，使边缘看起来处于流体静力平衡状态。然而，在平衡假设下，根据该扇区的数据得出的总质量分布显示出2倍的非物理跳跃，边缘内的质量较低。我们认为，较冷的气体在团簇引力势垒中“晃动”，现在位于最大位移点附近，在那里它的速度为零，但向心加速度为非零。这种非静力气体的分布应该反映了加速参考系中重力的减少，从而导致了明显的质量不连续。假定边缘外的气体是流体静力学的，运动气体的加速度可由质量跳跃估计，约800h公里S-1(108年)-1。这种气体可用于消散的引力势能大约是其当前热能的一半。从CD星系延伸出来的冷丝的长度(Fabian等人)可以给出气体晃动的幅度，30-40小时-1kpc。这种气体整体运动可能是由过去的亚星系团坠落对中心引力势的扰动引起的。
Chandra data on A1795 reveal a mild edge-shaped discontinuity in the gas density and temperature in the southern sector of the cluster at r = 60 h-1 kpc. The gas inside the edge is 1.3-1.5 times denser and cooler than outside, while the pressure is continuous, indicating that this is a "cold front," the surface of contact between two moving gases. The continuity of the pressure indicates that the current relative velocity of the gases is near zero, making the edge appear to be in hydrostatic equilibrium. However, a total mass profile, derived from the data in this sector under the equilibrium assumption, exhibits an unphysical jump by a factor of 2, with the mass inside the edge being lower. We propose that the cooler gas is "sloshing" in the cluster gravitational potential well and is now near the point of maximum displacement, where it has zero velocity but nonzero centripetal acceleration. The distribution of this nonhydrostatic gas should reflect the reduced gravity force in the accelerating reference frame, resulting in the apparent mass discontinuity. Assuming that the gas outside the edge is hydrostatic, the acceleration of the moving gas can be estimated from the mass jump, a ~ 800 h km s-1 (10 8 yr)-1. The gravitational potential energy of this gas that is available for dissipation is about half of its current thermal energy. The length of the cool filament extending from the cD galaxy (Fabian et al.) may give the amplitude of the gas sloshing, 30-40 h-1 kpc. Such gas bulk motion might be caused by a disturbance of the central gravitational potential by past subcluster infall.