AGN feedback in galaxy groups: the delicate touch of self-regulated outflows
AGN feedback in galaxy groups: the delicate touch of self-regulated outflows
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星系群中的活动星系核反馈：自我调节流出的微妙触感
DOI：
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发表时间：
2011
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通讯作者：
C. Melioli
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作者：
M. Gaspari;F. Brighenti;A. D'ercole;C. Melioli
活动星系核（AGN）通过大量次相对论外流加热，可能是解决宇宙学系统中长期存在的“冷却流问题”的关键。在以前的论文中，我们表明，冷吸积反馈，并在较小程度上，邦迪自我调节模型实际上是能够淬火冷却速率为几个陀螺仪，在同一时间保存的主要冷核心功能，如观察到的密度和温度分布。对于较轻的系统，例如星系群，也是如此吗？答案在全球范围内都是肯定的，尽管存在显著差异。采用修改版本的自适应网格加密代码FLASH 3.2，我们发现，成功的三维模拟冷和邦迪模型几乎收敛的星系群环境中，与机械效率的范围分别为5 × 10 ―4 ―10 ―3和5 × 10 ―2 ―10 ―1。星系群的演化故事线主要是由亚爱丁顿流出的准连续温和注入（机械功率P = 10 44 erg s-1，v = 10 4 km s-1）。冷和混合吸积模型，此外，非常短的静止期，其次是适度的爆发（10倍的前一阶段），产生一系列的10-20千秒差距大小的空腔，高密度对比度，温度类似于周围介质和冷轮辋。冲击加热后，一个阶段的湍流促进气体的混合和金属的扩散，其峰值沿着射流轴（高达40千秒差距）在活动阶段。在这个阶段，由持久的外流产生的隧道（在模拟X射线表面亮度图中很难检测到）很容易破碎，产生微小的浮力气泡，通常大小为几千秒差距。与星系团相反，活动星系核的自我调节反馈必须是持久的，具有“微妙的触感”，而不是罕见的爆炸性中风。这种演化上的差异决定了星系群并不是星系团的缩小版本：活动星系核的加热可能在不同的机制中运作，这有助于观察到的自相似性破缺。
Active galactic nucleus (AGN) heating, through massive subrelativistic outflows, might be the key to solve the long-lasting 'cooling flow problem' in cosmological systems. In a previous paper, we showed that cold accretion feedback and, to a lesser degree, Bondi self-regulated models are in fact able to quench cooling rates for several Gyr, at the same time preserving the main cool-core features, like observed density and temperature profiles. Is it true also for lighter systems, such as galaxy groups? The answer is globally yes, although with remarkable differences. Adopting a modified version of the adaptive mesh refinement code FLASH 3.2, we found that successful 3D simulations with cold and Bondi models are almost convergent in the galaxy group environment, with mechanical efficiencies in the range 5 x 10 ―4 ―10 ―3 and 5 x 10 ―2 ―10 ―1 , respectively. The evolutionary storyline of galaxy groups is dominated by a quasi-continuous gentle injection with sub-Eddington outflows (with the mechanical power P ∼ 10 44 erg s ―1 , v ∼ 10 4 km s ―1 ). The cold and hybrid accretion models present, in addition, very short quiescence periods, followed by moderate outbursts (10 times the previous phase), which generate a series of 10-20 kpc size cavities with high density contrast, temperatures similar to the ambient medium and cold rims. After shock heating, a phase of turbulence promotes gas mixing and diffusion of metals, which peak along the jet-axis (up to 40 kpc) during active phases. At this stage, the tunnel, produced by the enduring outflow (hard to detect in the mock X-ray surface brightness maps), is easily fragmented, producing tiny buoyant bubbles, typically a few kpc in size. In contrast to galaxy clusters, the AGN self-regulated feedback has to be persistent, with a 'delicate touch', rather than rare and explosive strokes. This evolutionary difference dictates that galaxy groups are not scaled-down versions of clusters: AGN heating might operate in different regimes, contributing to the self-similarity breaking observed.