Driving hot and cold gas flows in galaxies with feedback from massive black holes

现代天文学试图了解我们在宇宙大爆炸后的130亿年里，我们在局部宇宙中看到的星系和大型星系团是如何形成的。包括重力和气体冷却等关键物理原理在内的计算机模拟可以成功地在大尺度上再现星系和星系团的分布。然而，这些模型无法恢复单个星系的结构。特别是，这些模型预测了星系中过多的气体冷却，产生了大型冷气藏和巨大的恒星形成爆发，而这些都没有被观察到。需要加热装置来防止这种情况。虽然低质量星系可以被恒星和超新星的风加热，但大质量星系需要在超大质量黑洞周围的强引力环境中发射更强大的高能粒子射流。这些黑洞的质量是太阳的100万到数十亿倍，位于包括银河系在内的每个星系的中心。然而，我们还不明白一个太阳系大小的黑洞是如何在大约10亿倍大的尺度上加热整个星系及其周围环境的。超大质量黑洞的能量反馈是星系演化中最重要的未解决问题之一，也是本提案的重点。恒星的形成和黑洞的活动都是由大质量星系中心的冷气体推动的，这些星系的详细结构现在可以通过新的ALMA天文台来解决。ALMA是位于智利阿塔卡马沙漠的一个由66个高精度射电天线组成的大型阵列，它通过提供近宇宙和遥远宇宙中最令人难以置信的寒冷气体的详细视图，改变了我们对星系演化的理解。在ALMA四年的科学运行中，我领导了对五个最巨大的富含气体的星系的分析，这些星系在调试的早期科学阶段被“高优先级”观测到。我是三个新项目的负责人，另外六个项目的合著者，我领导了对ALMA四个观测周期的观测结果的分析。在观测到的6个星系中，有5个星系的冷分子气体长丝延伸的距离相当于银河系的直径，并在被喷流膨胀的巨大射电等离子体气泡周围形成明亮、寒冷的边缘。这些巨大气泡的膨胀将大量的热量输送到周围环境，从而抑制了气体的冷却，但我现在的研究结果表明，这些气泡也会从星系中心提升大量的气体流。随后，气体以循环流的形式落回中央气体盘。这些冷气体盘为超大质量黑洞提供燃料，从而维持了喷流，限制了宿主星系中的恒星形成。在接下来的五年里，我将把我的探路者观测扩展到一个大的星系样本，主要目标是了解冷气体的起源，追踪为超大质量黑洞提供食物的气体流入，并确定喷射的气泡如何通过从星系核心提升气体来调节恒星形成和黑洞活动。我的分析将集中在绘制延伸细丝中的气体速度图，以确定它们如何被气泡提升，并确定喷射功率与气体流出的质量、速度和程度之间的关系，这些关系可以纳入星系模拟。我还将研究随后流入中央圆盘的气体的结构，以显示来自超大质量黑洞的反馈如何能够持续限制星系的增长。

Modern astronomy seeks to understand how the galaxies and large clusters of galaxies that we see in the local universe formed in the thirteen billion years since the Big Bang. Computer simulations that include the key physics of gravity and gas cooling can successfully reproduce the distribution of galaxies and clusters on large scales. However, these models fail to recover the structure of individual galaxies. In particular, the models predict too much gas cooling in galaxies producing large cold gas reservoirs and huge bursts of star formation, which are not observed. A heating mechanism is required to prevent this. Whilst low mass galaxies can be heated by winds from stars and supernovae, massive galaxies require the much more powerful jets of high-energy particles launched in the strong gravitational environment around a supermassive black hole. These black holes are a million to several billion times the mass of our Sun and sit at the centre of every galaxy, including our Milky Way. However, we do not yet understand how a black hole that is the size of the solar system is able to heat an entire galaxy and its surroundings on scales roughly a billion times larger. Energetic feedback from a supermassive black hole is one of the most important unsolved problems in galaxy evolution and is the focus of this proposal.Both the star formation and black hole activity are fuelled by cold gas at the centres of massive galaxies, whose detailed structure can now be resolved by the new ALMA Observatory. ALMA is a large array of 66 high precision radio dishes located in the Atacama Desert of Chile that is transforming our understanding of galaxy evolution by providing the most incredibly detailed view of cold gas in the nearby and distant universe. Over ALMA's four years of science operations, I have led the analyses of five of the most massive gas-rich galaxies that were observed at 'high priority' during the early science phase of the commissioning. I am the PI of three new programs, a co-author of a further six programs and I have led the analysis of observations from each of the four ALMA observing cycles so far. In five of the six galaxies observed, large filaments of cold molecular gas extend a distance equivalent to the diameter of the Milky Way, and form bright, cold rims around giant bubbles of radio-emitting plasma inflated by the jet. The inflation of these huge bubbles pumps a substantial amount of heat into the surroundings that suppresses gas cooling, but my results now show that the bubbles also lift massive gas flows from the galaxy centre. The gas later falls back in a circulating flow feeding central gas disks. These cold gas disks fuel supermassive black holes, thereby sustaining jets and limiting star formation in the host galaxies.Over the next five years, I will expand my pathfinder observations to a large sample of galaxies with the primary goals of understanding the origin of the cold gas, tracing gas inflows that feed supermassive black holes and determining how the jet-blown bubbles regulate star formation and black hole activity by lifting gas from the galaxy's core. My analysis will focus on mapping the gas velocities in the extended filaments to determine how they can be lifted by the bubbles and identifying correlations between the jet power and the mass, velocity and extent of gas outflows that can be incorporated into galaxy simulations. I will also study the structure of subsequent inflows of gas feeding central disks to show how this feedback from a supermassive black hole can be sustained to restrict the growth of galaxies.