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，很大一部分星系团的中心冷却时间很短。然而，没有观察到恒星形成的程度和随后应该存在的冷气体的数量，这意味着加热机制正在发挥作用。来自中央活动星系核以相对论喷流形式的反馈预计将在这里发挥主导作用，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。这些星团中所体现的物理过程之间相互作用的复杂性使得分析模型变得棘手。这使得星系形成模拟处于独特的地位，因为它们可以深入了解现实环境中 AGN 射流反馈如何调节加热和冷却。然而，相关过程的作用范围跨越了许多数量级。喷气机在靠近 BH 地平线的地方发射并传播到很远的距离。气体从 ICM 流入，最终，吸积盘中的微观过程决定了该气体供给 BH 的速率。因此，从第一原理模拟这一点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，我的目标是推进目前对 AGN 吸积和反馈以及这种反馈能量耦合到 ICM 的机制的理解，我将通过开发新方法来改进其在星系形成的流体动力学模拟中的建模来实现这一点。 移动网格代码，AREPO，我将利用：a）新的 AGN 吸积模型，其中超拉格朗日细化技术允许从星系尺度一直到吸积盘的外边缘跟踪质量和角动量流。然后通过将其与亚网格薄阿尔法圆盘耦合来自洽地跟踪 BH 质量和自旋。 b) 一个新的 AGN 射流模型，它也利用了超拉格朗日精化，在这里能够在秒差距尺度上喷射射流，并且随后的演化可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 BH 自旋耦合，利用 Blandford-Znajek (BZ) 机制自洽地预测其功率。因此，我们将第一次能够研究 BZ 喷流的反馈如何影响星团尺度上的结构。我将首先在一个孤立的核周盘中测试模型，准确地跟踪亚网格吸积盘的演化、BH 质量和自旋以及喷流的传播。接下来，我将考虑中心蕴藏着吸积超大质量黑洞的孤立星系团的重大合并，以研究合并事件期间喷流功率和方向如何变化，以及这是否可以解释 X 形射电星系的出现。作为最后一步，我将使用 BZ 喷气机对星团形成进行完全自洽的宇宙学模拟，以研究这些源无线电功率的宇宙演化以及从 FRII 到 FRI 射电星系的可能过渡。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 SKA 望远镜的预测。