AGN Heating in Simulated Cool-core Clusters
AGN Heating in Simulated Cool-core Clusters
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DOI：
10.3847/1538-4357/aa88c1
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发表时间：
2016-11
期刊：
影响因子：
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通讯作者：
Yuan Li;M. Ruszkowski;G. Bryan
中科院分区：
文献类型：
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作者：
Yuan Li;M. Ruszkowski;G. Bryan
我们分析加热和冷却过程中的一个理想化的模拟冷核心集群，动量驱动的活动星系核反馈平衡辐射冷却的时间平均意义上。我们发现，平均而言，通过冲击波的能量耗散几乎是一个数量级高于通过湍流。模拟中的大多数冲击波都是马赫数小于1.5的非常弱的冲击波，但是更强的冲击波虽然很少，但更有效地耗散能量。我们发现，冲击耗散是一个陡峭的函数的半径，与大多数的能量耗散在30千秒差距，空间集中比辐射冷却损失。然而，绝热过程和（激波后物质和周围气体的）混合能够将热量重新分配到整个核心。活动星系核能量的相当一部分也逃逸出核心区域。这个星系团经历了活动星系核爆发的循环，伴随着降水增强和星星形成的时期，时间跨度超过了十亿年。在活动星系核爆发的高峰期，星系团核心处于过热状态，而在活动星系核爆发的末期，星系团核心处于欠热状态。在加热占主导地位的阶段，湍流耗散本身往往能够平衡每个半径的辐射冷却，但当这种情况发生时，冲击波不可避免地耗散更多的能量。我们的模拟解释了为什么有些星系团，如阿贝尔2029，是冷却为主，而在其他一些星系团，如英仙座，各种加热机制，包括冲击加热，湍流耗散和气泡混合都可以单独平衡冷却，并在一起，过热的核心。
We analyze heating and cooling processes in an idealized simulation of a cool-core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense. We find that, on average, energy dissipation via shock waves is almost an order of magnitude higher than via turbulence. Most of the shock waves in the simulation are very weak shocks with Mach numbers smaller than 1.5, but the stronger shocks, although rare, dissipate energy more effectively. We find that shock dissipation is a steep function of radius, with most of the energy dissipated within 30 kpc, more spatially concentrated than radiative cooling loss. However, adiabatic processes and mixing (of post-shock materials and the surrounding gas) are able to redistribute the heat throughout the core. A considerable fraction of the AGN energy also escapes the core region. The cluster goes through cycles of AGN outbursts accompanied by periods of enhanced precipitation and star formation, over gigayear timescales. The cluster core is under-heated at the end of each cycle, but over-heated at the peak of the AGN outburst. During the heating-dominant phase, turbulent dissipation alone is often able to balance radiative cooling at every radius but, when this is occurs, shock waves inevitably dissipate even more energy. Our simulation explains why some clusters, such as Abell 2029, are cooling dominated, while in some other clusters, such as Perseus, various heating mechanisms including shock heating, turbulent dissipation and bubble mixing can all individually balance cooling, and together, over-heat the core.