[论文解读] Cluster Heating by Viscous Dissipation of Waves

Mateusz Ruszkowski, M. Brüggen+1 more|arXiv (Cornell University)|Oct 27, 2003

Material Science and Thermodynamics被引用 1

一句话总结

本文表明，星系团中由间歇性AGN活动产生的波的黏性耗散可提供足够的加热以抵消辐射冷却，从而实现准稳定的冷却流抑制。使用FLASH进行的模拟显示，剪切黏度下存在空间分布均匀、无激波的加热，其达到平衡的时间快于冷却 timescales，间歇性AGN活动对于有效黏性加热至关重要。

ABSTRACT

We simulate the effects of viscous dissipation of waves that are generated by AGN activity in clusters of galaxies. We demonstrate that the amount of viscous heating associated with the dissipation of these waves can offset radiative cooling rates in cooling flow clusters of galaxies. This heating mechanism leads to spatially distributed and approximately symmetrical dissipation. The heating waves reach a given distance from the cluster center on a timescale shorter than the cooling time. This means that this heating mechanism has the potential of quenching cooling flows in a quasi-stable fashion. Moreover, the heating is gentle as no strong shocks are present in the simulations. We first investigated whether a single continuous episode of AGN activity can lead to adequate dissipation to balance cooling rates. These simulations demonstrated that, whereas secondary waves generated by the interaction of the rising bubble with the intracluster medium are clearly present, viscous heating associated with the dissipation of these waves is insufficient to balance radiative cooling. It is only when the central source is intermittent that the viscous dissipation of waves associated with subsequent episodes of activity can offset cooling. This suggests that the ripples observed in the Perseus cluster can be interpreted as being due to the AGN duty cycle, i.e., they trace AGN activity history. The simulations were performed using the PPM adaptive mesh refinement code FLASH in two dimensions, including Spitzer (shear) viscosity but no bulk viscosity.

研究动机与目标

• 调查AGN活动产生的波的黏性耗散是否能平衡星系团中的辐射冷却。
• 确定AGN占空比在维持有效黏性加热中的作用。
• 评估波驱动的黏性加热是否能提供无强激波的空间分布且稳定的加热。
• 评估单次与间歇性AGN事件的黏性加热效率。
• 解释像Perseus这样的星系团中观测到的涟漪是否为AGN占空比历史的特征。

提出的方法

• 使用二维的PPM自适应网格细化代码FLASH进行模拟。
• 引入剪切（Spitzer）黏度以模拟星系团介质中波的黏性耗散。
• 排除体积黏度以隔离剪切黏度的影响。
• 将AGN活动建模为单次连续事件或间歇性爆发。
• 跟踪波的传播和黏性加热随时间的变化，以与冷却速率进行比较。
• 分析加热的空间分布和 timescale 相对于冷却 timescale 的特性。

实验结果

研究问题

• RQ1 AGN活动产生的波的黏性耗散是否能平衡星系团中辐射冷却速率？
• RQ2 间歇性AGN活动是否比单次连续事件产生更有效的黏性加热？
• RQ3 黏性加热达到平衡的时间与冷却 timescale 相比如何？
• RQ4 黏性加热是否能提供无强激波的空间分布且对称的加热？
• RQ5 像Perseus星系团中观测到的涟漪是否通过波的耗散反映出AGN占空比？

主要发现

• 波耗散产生的黏性加热可抵消冷却流星系团中的辐射冷却速率。
• 单次连续AGN事件因波生成和耗散不足，无法产生足够的黏性加热。
• 间歇性AGN活动通过多次事件的累积波耗散，实现了有效的黏性加热。
• 加热在任何给定半径上的达到时间短于冷却 timescale，从而实现快速稳定。
• 该加热机制温和，模拟中未出现强激波。
• Perseus星系团中观测到的涟漪可能反映了AGN占空比，因其与周期性活动引起的波耗散一致。