The role played by super massive black holes in magnetizing the circum-galactic medium

环星系介质（CGM）是星系形成和演化的关键，因为它提供了对恒星和超大质量黑洞（SMBH）反馈过程的直接约束，人们普遍认为这些反馈过程调节着星系的整体特性（质量、大小、形态）。然而，旨在捕捉这些反馈过程的详细数值流体动力学模拟迄今未能产生与高红移星系周围观测到的CGM相匹配的CGM。这种失败可能反映了这样一个事实，即恒星形成和恒星反馈，以及SMBH的形成、吸积和反馈，都发生在极小的亚星系尺度上，这使得在解决星系更大尺度环境的同时，以合理的精度对它们进行模拟是一个巨大的挑战。多亏了一种超级拉格朗日精细技术，专门用于提高CGM的数值分辨率，再加上一种精确的辐射传输方法，可以自一致地跟踪电离光子与气体的相互作用，我们最近开始着手的NEPHTHYS宇宙学缩放模拟套件已经开始补救这种情况。事实上，这种方法第一次揭示了CGM中与观测到的相当的丰富特征。另一方面，模拟中仍然缺少重要的物理现象。特别是，磁场对CGM结构的影响仍然是未知的领域。磁场被测量为与星系星际介质中的热能量和湍流能量均分。与此同时，关于这些场在塑造星系演化中所起作用的理论预测无疑将有助于理解即将彻底改变该领域的前所未有的深射电数据。因此，哲学博士项目包括两个阶段。首先，学生将扩展NEPHTHYS的高分辨率宇宙学模拟套件，目标是大质量星系的CGM，通过运行它们的MHD对应，包括SMBH吸积和反馈，建立在我们小组以前开发的最先进的算法之上。其次，他们将基于这些MHD模拟的后处理开发他们自己的星系同步辐射模型，以期为即将到来的平方公里阵列仪器及其前身（与牛津大学以Jarvis教授为中心的射电天文观测小组互动）产生真实的模拟观测数据。这项研究属于STFC的科学计划挑战A：宇宙是如何开始的以及它是如何演变的？，以及更具体的子挑战A.4：第一批恒星、黑洞和星系是何时以及如何诞生的？A.5：恒星和星系是如何演化的？

The circum-galactic medium (CGM) holds the key to galaxy formation and evolution as it provides direct constrains on the stellar and supermassive black hole (SMBH) feedback processes widely believed to regulate galaxy global properties (mass, size, morphology). Yet, detailed numerical hydrodynamics simulations designed to capture these feedback processes have so far failed to produce a CGM which matches that observed around high-redshift galaxies. Presumably this failure reflects the fact that star formation and stellar feedback, and SMBH formation, accretion and feedback, take place on extremely small, sub-galactic scales, making it a tremendous challenge for simulations to model them with reasonable accuracy whilst resolving the galaxy larger scale environment at the same time. Thanks to a super Lagrangian refinement technique specifically tuned to increase numerical resolution in the CGM, coupled to an accurate radiative transfer method to self-consistently follow the interaction of ionising photons with the gas, the NEPHTHYS suite of cosmological zoom simulations we have recently embarked upon has started to remedy the situation. Indeed, such an approach has, for the first time, revealed a richness of features in the CGM comparable to that observed. On the other hand, important physics is still missing from the simulations. In particular, the impact of magnetic fields --- which are measured to be in equipartition with thermal and turbulent energy in the interstellar medium of galaxies --- on the structure of the CGM remains uncharted territory. Meanwhile, theoretical predictions regarding the role these fields play in shaping galaxy evolution will undoubtedly be required to help make sense of the unprecedentedly deep radio data soon to revolutionize the field. The DPhil project therefore consists of two stages. At first, the student will expand the NEPHTHYS suite of high-resolution cosmological simulations targetting the CGM of massive galaxies, by running their MHD counterpart and including SMBH accretion and feedback, building upon state-of-the-art algorithms previously developed within our group. Secondly, they will develop their own model for galaxy synchrotron emission based on the post-processing of these MHD simulations, in a view to produce realistic mock observational data for the coming Square Kilometer Array instrument and its precursors (in interaction with the radio astronomy observational group at Oxford centred around Prof. Jarvis). This research falls within STFC's science programme challenge A: How did the Universe begin and how it is evolving?, and more specifically sub-challenges A.4: When and how were the first stars, black holes and galaxies born? and A.5: How do stars and galaxies evolve?