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arXiv 2409.18271astro-ph.GA
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气体冷却与湍流对AGN驱动外流性质的复杂影响

The complex effect of gas cooling and turbulence on AGN-driven outflow properties

K. Zubovas, M. Tartėnas, M. A. Bourne

AI总结:

本文通过理想化流体动力学模拟研究了湍流与冷却对千秒差距尺度AGN风驱动外流的影响,发现冷却显著降低外流能量率,且冷却与湍流的相互作用依赖于AGN光度,同时指出使用可观测性质会低估参数。

摘要:

(节略)近爱丁顿速率的超大质量黑洞(SMBH)吸积可通过强风影响宿主星系。此类风的理论模型可解释SMBH与宿主星系间的观测相关性,以及若干活动星系中观测到的强大多相外流。解析模型通常假设球对称及具有绝热状态方程的光滑气体分布。然而,真实星系的星际介质是团块状的且冷却效应显著,使分析复杂化。我们采用一套理想化流体动力学模拟,以分离湍流与冷却对千秒差距尺度上AGN风驱动外流的发展及全局性质的影响。我们测量了系统演化1.2 Myr期间的外流速度、质量外流率、动量与能量负载因子,并估算了合理的观测推导值。我们发现绝热模拟近似重现了外流性质的解析估计,且与湍流或团块度无关。然而,冷却使光滑模拟中的外流能量率降低1-2个数量级,在湍流模拟中降低达一个数量级。冷却与湍流的相互作用取决于AGN光度:在爱丁顿极限AGN中,湍流增强了AGN风与气体的耦合,而在较低光度模拟中则相反。这是因为致密气体团块能抵抗低光度AGN反馈,但会被高光度AGN反馈驱散。模拟中多相外流气体的整体性质与多相外流观测定性一致。我们还发现,使用“可观测”外流性质会导致其参数相比真实值被低估数倍。

英文摘要:

(abridged) Accretion onto supermassive black holes (SMBHs) at close to the Eddington rate can influence the host galaxy via powerful winds. Theoretical models of such winds can explain observational correlations between SMBHs and their host galaxies and the powerful multi-phase outflows observed in a number of active galaxies. Analytic models usually assume spherical symmetry and a smooth gas distribution with an adiabatic equation of state. However, the interstellar medium in real galaxies is clumpy and cooling is important, complicating the analysis. We used a suite of idealised hydrodynamical simulations to isolate the effects of turbulence and cooling on the development and global properties of AGN wind-driven outflows on kiloparsec scales. We measured the outflow velocity, mass outflow rate and momentum and energy loading factors as the system evolved over 1.2 Myr and estimated plausible observationally derived values. We find that adiabatic simulations approximately reproduce the analytical estimates of outflow properties independently of turbulence or clumpiness. However, cooling reduces the outflow energy rate by 1-2 orders of magnitude in the smooth simulations and by up to one order of magnitude in the turbulent ones. The interplay between cooling and turbulence depends on AGN luminosity: in Eddington-limited AGN, turbulence enhances the coupling between the AGN wind and the gas, while the opposite happens in lower-luminosity simulations. This occurs because dense gas clumps are resilient to low-luminosity AGN feedback but get driven away by high-luminosity AGN feedback. The overall properties of multi-phase outflowing gas in our simulations qualitatively agree with observations of multi-phase outflows. We also find that using `observable' outflow properties leads to their parameters being underestimated by a factor of a few compared with real values.

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