The distribution of black hole growth across the evolving galaxy population

了解星系如何随时间形成和演化是天体物理学中最重要和最复杂的挑战之一。在每个星系的中心(包括我们自己的星系，银河系)，都被认为有一个质量是太阳一百万到十亿倍的大黑洞。现在人们认为，这些大质量的黑洞可以决定它们所在星系的大部分结构和演化，尽管确切的方式和原因仍不清楚。我的研究重点是星系和黑洞之间的这些重要联系。特别是，我研究了星系，在那里，黑洞随着物质的坠落而迅速增长。在坠入之前，这种物质会变热，在整个电磁频谱上释放出大量的辐射。黑洞以这种方式增长的星系被描述为有一个活跃的星系核。我的目标是理解为什么一些星系有这些活跃的核，而在其他星系(如银河系)，黑洞并没有快速增长。一些机制必须将物质驱动到星系的中心区域，并为黑洞的增长提供动力，但我们还不确定这些机制是什么。此外，随着黑洞的增长，释放出的巨大能量可能会对银河系的其他部分产生重大影响，加热或喷射气体，阻止新恒星的形成。因此，确定黑洞在星系寿命内增长的时间对于理解星系演化的物理学至关重要。我最近的工作表明，活动核(由不断增长的黑洞提供动力)可能会在数十万年的时间尺度上断断续续地闪烁，与星系的寿命相比，这是相对较短的。这种闪烁使得将黑洞增长的总体水平与星系人口的演化联系起来变得更加困难。为了取得进展，我们需要测量黑洞增长率在类似演化阶段的大样本星系上的*分布。到目前为止，绘制如此详细的黑洞增长分布图一直很困难，因为星系样本的大小有限，而且缺乏灵敏的X射线观测，需要这些观测来窥视星系中心并测量当前中央黑洞的增长速度。在接下来的几年里，这种情况将发生巨大变化。一台新的太空望远镜eROSITA将绘制整个天空的X射线波长图，我将用它来以前所未有的细节跟踪附近星系内的黑洞增长率。这些研究尤其重要，因为黑洞的影响似乎在附近宇宙中最大的星系中最为严重。这些星系通常是圆形的，红色的，不会形成任何新的恒星--这可能都是由于中心的黑洞。此外，我们正在用最大的地面望远镜进行新的调查，测量来自极暗的遥远星系的大样本的光的光谱，从而揭示出宇宙不到当前年龄的一半时星系的演化周期。我将把这些新的暗淡星系调查与最高质量的X射线数据(来自NASA的钱德拉望远镜)结合起来，追踪黑洞在这一重要的宇宙早期时期的增长。这些研究的结合将提供推动黑洞增长的物理机制的全面图景，以及黑洞对星系演化的影响，从早期宇宙到最近的宇宙时代。

Understanding how galaxies form and evolve over time is one of the most important and complicated challenges in astrophysics. At the centre of every galaxy (including our own galaxy, the Milky Way) there is thought to be a massive black hole that is a million to a billion times the mass of the Sun. It is now thought that these massive black holes could determine much of the structure and evolution of the galaxies which host them, although exactly how and why is still unclear.My research focuses on these important connections between galaxies and black holes. In particular, I study galaxies where the black hole is rapidly growing as matter falls in. Before falling in, this matter gets hot, emitting huge amounts of radiation over the entire electromagnetic spectrum. A galaxy where the black hole is growing in this way is described as having an active galactic nucleus. I aim to understand why some galaxies have these active nuclei, whereas in other galaxies (such as the Milky Way) the black hole is not rapidly growing. Some mechanisms must drive material into the central regions of a galaxy and fuel this black hole growth, but we are not yet sure what these mechanisms are. Furthermore, the huge amounts of energy released as the black hole grows could have a significant impact on the rest of the galaxy, heating up or ejecting gas and preventing the formation of new stars. Thus, determining when black hole growth occurs within the lifetimes of galaxies is vital to understand the physics of galaxy evolution. My recent work has shown that active nuclei (powered by growing black holes) may flicker on and off over timescales of a few hundred thousand years, which is relatively short compared to the lifetime of a galaxy. This flickering makes it much harder to link the overall levels of black hole growth to the evolution of the galaxy population. To make progress, we need to measure the *distribution* of black hole growth rates over large samples of galaxies in similar evolutionary phases. Mapping the distribution of black hole growth in such detail has, until now, been difficult due to the limited size of galaxy samples and the lack of sensitive X-ray observations that are needed to peer into the centres of galaxies and measure the current growth rate of the central black hole.Over the next few years, this situation will change dramatically. A new space telescope, eROSITA, will map the entire sky at X-ray wavelengths, which I will use to track black hole growth rates within nearby galaxies in unprecedented detail. These studies are particularly important, as the impact of black holes appears to be most severe in the biggest galaxies in the nearby Universe. These galaxies are generally round in shape, red in colour, and tend not to be forming any new stars - possibly all due to the black hole at the centre.In addition, new surveys are underway with our largest ground-based telescopes, measuring the spectrum of light from large samples of extremely faint, distant galaxies and thus revealing the evolutionary lifecycles of galaxies when the Universe was less than half its current age. I will combine these new faint galaxy surveys with the highest quality X-ray data (from NASA's Chandra telescope) to track black hole growth during this important early epoch of cosmic time. The combination of these studies will provide a comprehensive picture of the physical mechanisms that drive black hole growth and the impact of black holes on the evolution of galaxies, spanning from the early Universe to recent cosmic times.