Next generation hydrodynamic simulations of galaxy clusters

星系团拥有宇宙中最大质量的星系，恒星质量高达太阳质量的一万亿倍。这些星系周围是巨大的热的、发射X射线的等离子体蓄水池，温度超过1000万开尔文。然而，一个令人费解的观察是，这种气体并没有以预期的速度冷却并形成新的恒星--为什么大质量星系中的恒星形成停止了？一种目前被看好的答案是，气体是由活动星系核(AGN)通过发射射电明亮的相对论等离子体的强大喷流来保持热的。活动星系核由一个超大质量黑洞的吸积提供动力，在能量上能够抵消X射线气体中的辐射损失，甚至可以将一些气体完全赶出系统。星系团的现代流体动力学模拟试图包括这种所谓的活动星系核反馈过程的影响，并可以成功地模拟最亮星系团中恒星形成的关闭过程，同时产生具有观测合理质量的黑洞。然而，这些模拟目前很难再现气体的X射线热性质，预测物质往往太热，在星系团核心中扩散。这种差异很可能是因为目前的模型没有捕捉到所有的基本物理知识，但也可能是因为数值分辨率不够。在这个博士项目中，学生将加入正在进行的合作努力，利用SWIFT流体动力学代码(swft.du.ac.uk)开发具有更高分辨率和物理建模的新一代星系团模拟。他们将从事科学项目，包括分析新的模拟数据，并有机会帮助开发和测试新的模拟模型。该学生将加入处女座联盟，并使用DiRAC高性能计算设施(dirac.ac.uk)。

Galaxy clusters host the most massive galaxies in the Universe, with stellar masses up to one trillion times the mass of the Sun. These galaxies are surrounded by huge reservoirs of hot, X-ray emitting plasma, with temperatures over 10 million Kelvin. A puzzling observation, however, is that this gas is not cooling down and forming new stars at the expected rate - why does star formation shut down in massive galaxies? One, currently favoured, answer is that the gas is being kept hot by an active galactic nucleus (AGN) through the emission of powerful jets of radio-bright relativistic plasma. The AGN, powered by accretion on to a super-massive black hole, is energetically capable of counteracting the radiative losses in the X-ray gas and can even drive some of the gas out of the system altogether. Modern hydrodynamic simulations of galaxy clusters attempt to include the effects of this so-called AGN feedback process and can successfully model the shut-down of star formation in brightest cluster galaxies, while producing black holes with observationally-reasonable masses. However, these simulations currently struggle to reproduce the X-ray thermal properties of the gas, predicting material that tends to be too hot and diffuse in the cluster core. Such a discrepancy is likely the result of current models not capturing all the essential physics but may also be due to insufficient numerical resolution. In this PhD project, the student will join ongoing collaborative efforts to develop a new generation of cluster simulations with improved resolution and physics modelling using the SWIFT hydrodynamics code (swift.dur.ac.uk). They will work on science projects involving the analysis of new simulation data as well as have the opportunity to help develop and test new simulation models. The student will join the Virgo consortium and use the DiRAC high performance computing facility (dirac.ac.uk).