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arXiv 0906.3739astro-ph.COastro-ph.HE
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活动星系核的反馈效率

On the Feedback Efficiency of Active Galactic Nuclei

Ryuichi Kurosawa, Daniel Proga, Kentaro Nagamine

摘要:

我们测量和分析了相对大尺度外流中活动星系核辐射的能量、动量和质量反馈效率。我们的测量是基于轴对称和随时间变化的辐射流体动力学模拟最近在黑泽明和Proga。这些模拟遵循了在活动星系核辐射和中心10^8兆太阳黑洞引力影响下的气体动力学,尺度从~0.01到~ 10 pc。我们比较了我们的Mdot_a-rho_o关系与Bondi吸积模型预测的关系。对于与爱丁顿极限相当的高光度,幂律拟合(Mdot_a ~ rho_o^q)到我们的模型产生q=~0.5而不是由Bondi模型预测的q=1.0。这种差异是由外流造成的,外流对高光度下的总质量预算很重要。在我们的模型中发现的最大动量和质量反馈效率分别为~10^-2和~10^-1。然而,外流在能量上的重要性要小得多:以辐射光度为单位,它们的热功率和动能分别为~10^-5和~10^-4。的效率并不单调增加吸积光度,而是峰值周围的爱丁顿限制超过一个稳定的状态盘风样的解决方案存在。我们的能量反馈效率明显低于0.05,这是在一些宇宙学和星系合并模拟所需要的。这里发现的低反馈效率可能对早期宇宙中超大质量黑洞的质量增长有重大影响。然而,我们要强调的是,我们还没有考虑到吸积和外流的最里面的部分,在那里辐射和物质的相互作用最强烈。来自该区域的反馈可能具有显著高于此处发现的低值的效率。

英文摘要:

(Abridged) We measure and analyze the energy, momentum, and mass feedback efficiencies due to radiation from AGN in relatively large scale outflows. Our measurements are based on the axisymmetric and time-dependent radiation-hydrodynamical simulations recently presented in Kurosawa & Proga. These simulations follow dynamics of gas under the influences of the AGN radiation and the gravity of the central 10^8 Msun black hole on scales from ~0.01 to ~10pc. We compare our Mdot_a-rho_o relation with that predicted by the Bondi accretion model. For high luminosities comparable to the Eddington limit, the power-law fit (Mdot_a ~ rho_o^q) to our models yields q=~0.5 instead of q=1.0 which is predicted by the Bondi model. This difference is caused by the outflows which are important for the overall mass budget at high luminosities. The maximum momentum and mass feedback efficiencies found in our models are ~10^-2 and ~10^-1, respectively. However, the outflows are much less important energetically: their thermal and kinetic powers in units of the radiative luminosity are ~10^-5 and ~10^-4, respectively. The efficiencies do not increase monotonically with the accretion luminosity but rather peak around the Eddington limit beyond which a steady state disk-wind-like solution exists. Our energy feedback efficiencies are significantly lower than 0.05, which is required in some cosmological and galaxy merger simulations. The low feedback efficiencies found here could have significant implications on the mass growth of super massive black holes in the early universe. We stress however that we have not considered the innermost parts of the accretion and outflow where radiation and matter interact most strongly. The feedback from this region could have efficiencies significantly above the low values found here.

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