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

改进星系形成模拟中活动星系核反馈和吸积的处理。

• 批准号: 2114057
• 金额: --
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2114057
• 关键词: Improving; treatment; AGN; feedback; accretion

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.

X射线观测表明，相当一部分星系团的中心冷却时间很短。然而，没有观察到星星形成的程度和应该存在的冷气量，这意味着加热机制正在起作用。来自活动星系核中央的相对论性喷流形式的反馈在这里将发挥主导作用，然而反馈能量耦合到ICM的机制的相对重要性仍然是一个悬而未决的问题。这些星系团中物理过程之间相互作用的复杂性使得解析模型难以处理。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加热和冷却是如何通过AGN喷射反馈调节的。然而，相关过程所依据的尺度跨越了许多数量级。喷流在BH视界附近发射，并传播到很远的距离。气体从ICM汇集进来，最终，它是吸积盘中的微尺度过程，决定了这些气体进入BH的速率。因此，从第一性原理来模拟这一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，我的目标是推进目前对AGN吸积和反馈的理解，以及这种反馈能量耦合到ICM的机制，我将通过开发新的方法来改进它们在星系形成的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）一个新的活动星系核吸积模型，利用超拉格朗日精化技术，可以从星系尺度一直跟踪到吸积盘外缘的质量和角动量流动。BH的质量和自旋，然后跟踪自洽耦合这与一个子网格薄α盘。B）一个新的活动星系核喷流模型，它也使用了超拉格朗日修正，在这里，能够在秒差距尺度上注入喷流，并跟踪其随后的演变到数百千秒差距。我将使用这些模型作为一个框架，将喷流耦合到BH自旋，利用Blandford-Znajek（BZ）机制自洽地预测其功率。因此，对于第一次，我们将能够研究如何反馈从BZ喷流影响结构的集群scales.I将首先测试模型它在一个孤立的环核盘，准确地按照亚网格吸积盘的演变，BH质量和自旋以及传播的射流。接下来，我将考虑孤立星系团的主要合并，其中心藏有吸积超大质量黑洞，以研究合并事件期间喷气动力和方向的变化，如果这可以解释X形射电星系的发生。作为最后一步，我将进行完全自洽的宇宙学模拟的集群形成与BZ喷流研究宇宙的演变，这些来源的无线电功率和可能的过渡从FRII到FRI射电星系。我的模拟将允许对大量即将到来的无线电数据做出独特的预测，包括对SKA望远镜的预测。