为什么AGN和主机Galerkin未对齐？
Why Are AGN and Host Galaxies Misaligned?
摘要：
在观测上，由射电喷流和假定的环面追踪的活动星系核周围小尺度上的特征角动量轴与宿主星系的大尺度角动量轴没有很好的相关性。在本文中，我们表明，这样的错位自然出现在高分辨率的模拟，我们遵循角动量运输和流入从星系到亚pc尺度附近AGN，引发星系合并或孤立磁盘的不稳定性。突然的错位有时可能是由单个大质量团块稍微偏离轴落入中心引起的，但更普遍的是，即使气体流入是平滑的，并且只跟踪全球引力不稳定性，它们也会出现。当存在几个嵌套的自引力模式时，内部模式可以在外部模式的势中进动和翻滚。共振角动量交换可以在短时间内翻转或重新排列内模的自旋，即使没有大质量团块的存在。因此，我们并不认为活动星系核和它们的宿主星系会优先排列，也不认为这种相对排列是活动星系核燃料供应机制的一个指标。我们讨论了这一结论对活动星系核反馈和BH自旋演化的影响。这种错位可能意味着，即使是从光滑的大尺度盘吸积的黑洞也不会旋转到最大旋转，因此具有更适度的辐射效率和低效的喷流形成。如果在气体中存在进一步的、未分辨的团块，则可能出现更随机的取向，并且如果流入速度较慢且没有自引力，则可能发生更有序的吸积。
英文摘要：
It is well-established observationally that the characteristic angular momentum axis on small scales around AGN, traced by radio jets and the putative torus, is not well-correlated with the large-scale angular momentum axis of the host galaxy. In this paper, we show that such misalignments arise naturally in high-resolution simulations in which we follow angular momentum transport and inflows from galaxy to sub-pc scales near AGN, triggered either during galaxy mergers or by instabilities in isolated disks. Sudden misalignments can sometimes be caused by single massive clumps falling into the center slightly off-axis, but more generally, they arise even when the gas inflows are smooth and trace only global gravitational instabilities. When several nested, self-gravitating modes are present, the inner ones can precess and tumble in the potential of the outer modes. Resonant angular momentum exchange can flip or re-align the spin of an inner mode on a short timescale, even without the presence of massive clumps. We therefore do not expect that AGN and their host galaxies will be preferentially aligned, nor should the relative alignment be an indicator of the AGN fueling mechanism. We discuss implications of this conclusion for AGN feedback and BH spin evolution. The misalignments may mean that even BHs accreting from smooth large-scale disks will not be spun up to maximal rotation, and so have more modest radiative efficiencies and inefficient jet formation. Even more random orientations are possible if there is further, un-resolved clumpiness in the gas, and more ordered accretion may occur if the inflow is slower and not self-gravitating.
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