Magnetohydrodynamic relaxation of AGN ejecta: radio bubbles in the intracluster medium
Magnetohydrodynamic relaxation of AGN ejecta: radio bubbles in the intracluster medium
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AGN 喷射物的磁流体动力学弛豫：簇内介质中的射电气泡
DOI：
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
J. Braithwaite
中科院分区：
文献类型：
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作者：
J. Braithwaite
星系团的X射线图像经常显示低密度气泡，这些气泡显然是由活动星系核（AGN）流出物膨胀的。我认为这样一个气泡内的磁场的演变，使用分析和数值方法的混合。据发现，该领域放松到一个平衡，充满整个体积的气泡。这种情况发生的时间尺度主要取决于外流的磁化强度和螺旋度，以及周围星系团内介质（ICM）的性质。如果外流被强烈磁化，磁场在短时间尺度上经历重联，磁能转化为热能，同时场的特征长度尺度上升;当达到全局平衡时，这个过程停止。平衡场的强度取决于活动星系核注入磁泡的磁螺旋度：如果外流具有一致的净通量，因此具有大的螺旋度，那么在短时间尺度上将达到全球平衡，而低螺旋度外流导致没有达到全球平衡，并且在观测时重联将继续进行。然而，局部磁通管平衡将形成。另一方面，如果流出物的磁化非常弱，则不会发生重联，气泡内的磁场保持小尺度和被动。这些结果对气泡的内部组成，它们与ICM的相互作用-特别是解释气泡如何在ICM中移动很大的距离而不破裂-以及一般的冷却流问题都有影响。此外，气泡中的重连点可能是高能粒子的方便来源，避免了同步辐射器的寿命比它们所居住的气泡的年龄短的问题。
X-ray images of galaxy clusters often display underdense bubbles which are apparently inflated by active galactic nucleus (AGN) outflow. I consider the evolution of the magnetic field inside such a bubble, using a mixture of analytic and numerical methods. It is found that the field relaxes into an equilibrium, filling the entire volume of the bubble. The time-scale on which this happens depends critically on the magnetization and helicity of the outflow as well as on the properties of the surrounding intracluster medium (ICM). If the outflow is strongly magnetized, the magnetic field undergoes reconnection on a short time-scale, magnetic energy being converted into heat whilst the characteristic length-scale of the field rises; this process stops when a global equilibrium is reached. The strength of the equilibrium field is determined by the magnetic helicity injected into the bubble by the AGN: if the outflow has a consistent net flux and consequently a large helicity then a global equilibrium will be reached on a short time-scale, whereas a low-helicity outflow results in no global equilibrium being reached and at the time of observation reconnection will be ongoing. However, localized flux-tube equilibria will form. If, on the other hand, the outflow is very weakly magnetized, no reconnection occurs and the magnetic field inside the bubble remains small-scale and passive. These results have implications for the internal composition of the bubbles, for their interaction with the ICM – in particular to explain how bubbles could move a large distance through the ICM without breaking up – as well as for the cooling flow problem in general. In addition, reconnection sites in a bubble could be a convenient source of energetic particles, circumventing the problem of synchrotron emitters having a shorter lifetime than the age of the bubble they inhabit.
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DOI：
10.1111/j.1365-2966.2008.13162.x
发表时间：
2008-02
影响因子：
4.8
作者：
J. Croston;M. Hardcastle;M. Birkinshaw;D. Worrall;R. Laing
通讯作者：
J. Croston;M. Hardcastle;M. Birkinshaw;D. Worrall;R. Laing
X射线腔的演变
DOI：
10.1111/j.1365-2966.2009.14684.x
发表时间：
2009
影响因子：
4.8
作者：
Brüggen;Scannapieco
通讯作者：
Scannapieco
利用 Sunyaev-Zeldovich 效应对星系团 Abell 2163 进行多频率成像
影响因子：
6.5
作者：
通讯作者：
--
使用 APEX-SZ 测辐射热计成像数据对簇内气体进行非参数建模
影响因子：
6.5
作者：
通讯作者：
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