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局部宇宙中看到的星系和大星系团是如何在大爆炸以来的130亿年内形成的。计算机模拟包括重力和气体冷却的关键物理，可以成功地再现星系和星系团在大范围内的分布。然而，这些模型未能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，产生了大量的冷气藏和恒星形成的巨大爆发，而这些都没有被观测到。需要一种加热机制来防止这种情况发生。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的更强大的高能粒子喷流。这些黑洞的质量是太阳的一百万到几十亿倍，位于每个星系的中心，包括我们的银河系。然而，我们还不知道一个太阳系大小的黑洞是如何在大约10亿倍的尺度上加热整个星系及其周围的。来自超大质量黑洞的能量反馈是星系演化中最重要的悬而未决的问题之一，也是这一提议的焦点。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提供动力的，其详细结构现在可以通过新的ALMA天文台来解决。ALMA是一个由66个高精度射电天线组成的大阵列，位于智利的阿塔卡马沙漠，它提供了近宇宙和遥远宇宙中最详细的冷气体图像，正在改变我们对星系演化的理解。在ALMA四年的科学工作中，我领导了对五个质量最大、气体最丰富的星系的分析，这些星系在试运行的早期科学阶段被观测到了高度优先的地位。我是三个新项目的PI，另外六个项目的共同作者，到目前为止，我已经领导了对ALMA四个观测周期中每一个观测的分析。在观察到的六个星系中，有五个星系中有大的冷分子气体丝延伸的距离相当于银河系的直径，并在喷流膨胀的巨大射电发射等离子体气泡周围形成明亮的冷圈。这些巨大气泡的膨胀向周围注入了大量的热量，抑制了气体冷却，但我的结果现在表明，这些气泡也从银河系中心提升了大量的气体流动。气体随后回落到供应中央气体盘的循环流中。这些冷气体盘为超大质量黑洞提供燃料，从而维持喷流并限制宿主星系中恒星的形成。在接下来的五年里，我将把我的探路者观测扩大到大量星系样本，主要目标是了解冷气体的来源，追踪为超大质量黑洞提供燃料的气体流入，并确定喷出的气泡如何通过从银河系核心提升气体来调节恒星形成和黑洞活动。我的分析将重点放在绘制延长的细丝中的气体速度图，以确定它们如何被气泡提升，并确定喷流功率与气体外流的质量、速度和范围之间的关联，这些关联可以纳入星系模拟。我还将研究随后流入中央圆盘的气体的结构，以展示来自超大质量黑洞的反馈如何持续下去，以限制星系的增长。

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.