论辐照流中从高效线驱动到低效线驱动的转变
On the transition from efficient to inefficient line-driving in irradiated flows
AI总结：
本文通过黑体SED参数巡天与加热冷却平衡计算，确定AGN辐照流在约4×10^5 K以下转入低效线驱动，并用流体模拟揭示风性质变化。
摘要：
对电离活动星系核（AGN）外流的观测提供了令人信服的证据，表明辐射场会向等离子体传递动量和能量。在活动星系核中秒差距尺度的距离上，能量传递可能占据主导；在这种情况下，驱动外流所需的唯一作用力来自气体压力。在更靠近黑洞的位置，由于辐射加热不足，引力主导热能，气体处于所谓的“冷”状态。此时只有磁力或辐射力能够引发外流，但尚不清楚辐射力在何种温度和电离状态下减弱，因为这些性质取决于光谱能量分布（SED）。在本研究中，我们系统考察了由温度在约10^4–10^6 K范围内变化的黑体SED所产生的谱线辐射力的参数空间，以确定线驱动开始失去效率时的辐射温度。我们发现，温度≲4×10^5 K标志着向低效线驱动的转变。我们还自洽地计算了加热与冷却平衡，以估计气体温度，因此我们的参数考察覆盖了热驱动从可忽略不计变为与线驱动相当的转变过程。我们总结了大量径向流流体动力学模拟，以说明风的性质在转变过程中如何变化，以及这些性质对所假设的SED和主导流动参数的依赖。
英文摘要：
Observations of ionized AGN outflows have provided compelling evidence that the radiation field transfers both momentum and energy to the plasma. At parsec scale distances in AGN, energy transfer can dominate, in which case the only force needed to launch an outflow is that from gas pressure. Much closer to the black hole, gravity dominates thermal energy due to insufficient heating by the radiation and the gas is in the so-called `cold' regime. Only magnetic or radiation forces can then lead to outflow, but it is unclear at what temperature and ionization state the radiation force weakens, as these properties depend on the spectral energy distribution (SED). In this work, we survey the parameter space of radiation forces due to spectral lines resulting from blackbody SEDs with varying temperatures in the range $\sim 10^4 - 10^6$~K to identify the radiation temperature at which line-driving begins to lose efficiency. We find that the temperature $\lesssim4\times10^5$~K marks the transition to inefficient line driving. We also self-consistently compute the heating and cooling balance to estimate the gas temperature, so that our parameter survey covers the transition where thermal driving goes from negligible to comparable to line driving. We summarize a large set of hydrodynamical simulations of radial flows to illustrate how the wind properties change during the transition and the dependence of these properties on the assumed SED and governing flow parameters.
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