AGN活动：自调节回流
AGN activity: Self-regulation from backflow
摘要：
我们研究了由活动星系核在其宿主星系的ISM内发出的相对论性喷流所切割出的茧内的内循环。首先，我们开发了一个模型的内部流的起源，注意到一个显着增加的大规模的速度循环内的茧出现的密度和熵的显着梯度附近的热点（Crocco的涡产生定理的后果）。我们发现简单而准确的近似解的大规模流动，显示回流对几个内部秒差距区域的发展。我们解决了适当的流体动力学方程，我们使用这些解决方案来预测的质量流入率向中心区域。然后，我们使用FLASH 2.5对射流的传播进行了一系列二维模拟，以验证我们模型的预测。出现的回流以$0.1-0.8 \rm{M}_{\odot} \rm{yr.}^{-1}$量级的平均速率向活动星系核中心区域提供非常低角动量的气体，可以看出，确切的值强烈地依赖于中心ISM密度（对于固定的输入喷流功率）。这些流入的时间尺度显然弱依赖于射流/ISM参数，并为$3-5\times 10^{7} \rm{yrs}$的顺序。然后，我们认为，这些回流可以（至少部分）饲料的活动星系核，并提供了一个自我调节机制的活动星系核活动，这是不直接控制，而是控制，中央环核盘内的恒星形成率。
英文摘要：
We study the internal circulation within the cocoon carved out by the relativistic jet emanating from an AGN within the ISM of its host galaxy. Firstly, we develop a model for the origin of the internal flow, noticing that a significant increase of large scale velocity circulation within the cocoon arises as significant gradients in the density and entropy are created near the hot spot (a consequence of Crocco's vorticity generation theorem). We find simple and accurate approximate solutions for the large scale flow,showing that a backflow towards the few inner parsec region develops. We solve the appropriate fluid dynamic equations, and we use these solutions to predict the mass inflow rates towards the central regions. We then perform a series of 2D simulations of the propagation of jets using FLASH 2.5, in order to validate the predictions of our model. The backflows which arise supply the central AGN region with very low angular momentum gas, at average rates of the order of $0.1-0.8 \rm{M}_{\odot} \rm{yr.}^{-1}$, the exact value seen to be strongly dependent on the central ISM density (for fixed input jet power). The time scales of these inflows are apparently weakly dependent on the jet/ISM parameters, and are of the order of $3-5\times 10^{7} \rm{yrs}$. We then argue that these backflows could (at least partially) feed the AGN, and provide a self-regulatory mechanism of AGN activity, that is not directly controlled by, but instead controls, the star formation rate within the central circumnuclear disk.
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