Improving the treatment of AGN feedback and accretion in galaxy formation simulations.

x射线观测表明，很大一部分星系团的中心冷却时间很短。然而，恒星形成的程度和随后应该存在的冷气体的数量并没有被观测到，这意味着加热机制在起作用。来自中央AGN的反馈以相对论喷流的形式预计将在这里发挥主导作用，然而，通过反馈能量耦合到ICM的机制的相对重要性仍然是一个悬而未决的问题。在这些集群中表现出来的物理过程之间相互作用的复杂性使得分析模型难以处理。这使得星系形成模拟处于一个独特的位置，因为它们提供了在现实环境中AGN射流反馈如何调节加热和冷却的见解。然而，相关过程所依据的尺度跨越了许多数量级。喷流在黑洞视界附近发射，并传播到很远的地方。气体从ICM进入，最终，是吸积盘中的微观过程决定了这些气体进入黑洞的速度。因此，从第一性原理模拟这种情况所需的动态范围在计算上是不可行的，因此有必要调用所谓的“子网格”模型。在我的博士研究期间，我的目标是推进当前对AGN吸积和反馈的理解，以及这种反馈能量与ICM耦合的机制，我将通过开发新方法来改进他们在星系形成流体动力学模拟中的建模。使用最先进的移动网格代码AREPO，我将利用：a)一个新的AGN吸积模型，其中超拉格朗日精化技术允许质量和角动量流从星系尺度一直到吸积盘的外缘。通过将黑洞的质量和自旋与亚网格薄盘相结合，可以自洽地跟踪黑洞的质量和自旋。b)一种新的AGN射流模型，它也利用了超拉格朗日精化，在这里可以在秒差距尺度上注入射流，并将其随后的演变跟踪到数百千秒差距。我将使用这些模型作为框架，将射流与黑洞自旋耦合，利用Blandford-Znajek （BZ）机制自洽地预测其功率。因此，这是第一次，我们将能够研究BZ射流的反馈如何影响簇尺度上的结构。我将首先在一个孤立的环核圆盘上测试这个模型，准确地跟踪亚网格吸积盘的演变，黑洞的质量和自旋以及射流的传播。在此基础上，我将考虑在其中心容纳超大质量黑洞的孤立星系团的主要合并，以研究合并事件期间喷气动力和方向如何变化，以及这是否可以解释x形射电星系的出现。作为最后一步，我将用BZ射流对星团形成进行完全自洽的宇宙学模拟，以研究这些源的射电功率的宇宙演化以及从FRII到FRI射电星系的可能转变。我的模拟将允许对即将到来的大量射电数据做出独特的预测，包括对SKA望远镜的预测。

X-ray observations indicate that a significant fraction of galaxy clusters have short central cooling times. The degree of star formation and amount of cold gas that should then be present is not observed, however, implying that heating mechanisms are at work. Feedback from the central AGN in the form of relativistic jets is expected to play a dominant role here, however the relative importance of mechanisms through which the feedback energy couples to the ICM is still an open question.The complex nature of the interactions between the physical processes manifest in these clusters makes analytic models intractable. This puts galaxy formation simulations in a unique position as they provide insight into how heating and cooling are regulated by AGN jet feedback in a realistic environment. The scales on which the relevant processes act, however, span many orders of magnitude. Jets are launched close to the BH horizon and propagate to large distances. Gas is funnelled in from the ICM where, ultimately, it is micro-scale processes in the accretion disc that determine the rate at which this gas feeds the BH. The dynamic range required to simulate this from first-principles is therefore computationally unfeasible making it necessary to invoke so-called "sub-grid" models.During my PhD studies, I aim to advance current understanding of AGN accretion and feedback as well as the mechanisms by which this feedback energy couples to the ICM, which I will do by developing new methods to improve their modelling in hydrodynamic simulations of galaxy formation.Using the state-of-the-art moving-mesh code, AREPO, I will take advantage of: a) A new AGN accretion model whereby super-Lagrangian refinement techniques allow mass and angular momentum flows to be followed all the way from galaxy scales down to the outer edge of the accretion disc. The BH mass and spin are then tracked self-consistently by coupling this with a sub-grid thin alpha-disc. b) A new AGN jet model which also utilises super-Lagrangian refinement, here enabling the injection of the jet on parsec scales and its subsequent evolution to be followed to hundreds of kiloparsecs.I will use these models as a framework to couple the jet to the BH spin, taking advantage of the Blandford-Znajek (BZ) mechanism to self-consistently predict its power. So, for the first time, we will be in a position to study how feedback from a BZ jet affects structure on cluster scales.I will first test the model it in an isolated circumnuclear disc, accurately following the evolution of the sub-grid accretion disc, the BH mass and spin as well as the propagation of the jet. Following on from this, I will consider major mergers of isolated galaxy clusters harbouring accreting supermassive BHs at their centre to study how jet power and orientations changes during the merging event and if this can explain the occurrence of X-shaped radio galaxies. As a final step, I will perform fully self-consistent cosmological simulations of cluster formation with a BZ jet to study the cosmic evolution of radio power of these sources and a possible transition from FRII to FRI radio galaxies. My simulations will allow to make unique predictions for a wealth of upcoming radio data including the forecasts for the SKA telescope.