Revealing the hidden early lives of super-massive black holes

在宇宙中每一个大质量星系的中心都有一个超大质量黑洞（SMBH），其中一些黑洞的质量相当于100亿个太阳，而这个黑洞的体积与我们的太阳系差不多。当这些大黑洞通过吞噬周围的物质而成长时，会释放出大量的能量——使它们成为我们宇宙中最极端、最具能量的物体。除了本身是迷人的物体外，这些大黑洞还被认为在其宿主星系的演化中发挥着重要作用。如果我们想要完全了解像银河系这样的星系是如何形成的，我们就必须同时了解它们中心的大黑洞的形成和演化。近年来，观测研究已经能够越来越早地探索宇宙历史中SMBH的形成，揭示出惊人的巨大SMBH能够在当前宇宙年龄的前5%形成。然而，至关重要的是，我们对早期宇宙中这些怪物的了解仅限于非常明亮的光源——我们看到的只是冰山一角。我的研究计划的目标是建立一个SMBH形成早期阶段的完整图景-回答我们宇宙中最极端的物体是如何，何时以及在何处形成的问题。我的研究将使用泛欧射电望远镜低频阵列（LOFAR）进行的广泛的新射电天空调查，研究宇宙历史上活跃生长的黑洞，或活动星系核（AGN）。无线电观测的独特之处在于，它们可以透过掩盖黑洞吸积其他迹象的气体和尘埃，这意味着LOFAR能够揭示以前对我们隐藏的AGN活动。LOFAR的灵敏度和观测速度的结合意味着它现在发现了宇宙前30亿年里前所未有的AGN样本——这段宇宙历史时期被认为是最大和最极端的SMBH形成的时期。虽然LOFAR为我们在宇宙历史上发现AGN活动的能力提供了巨大的飞跃，但这些AGN的关键信息不能仅从它们的射电发射中获得。我们必须将这些数据与电磁频谱上的其他测量结果结合起来，以充分发挥其潜力。在我的欧内斯特卢瑟福奖学金期间，我将把LOFAR的无线电成像与新一代的互补天文调查结合起来，这将使我能够建立一个完整的统计图像，说明SMBH吸积活动是如何演变的，以及这与宿主星系本身的形成有何关系。这些调查的关键是WEAVE-LOFAR，这是一个为期五年的广泛项目，为超过一百万个LOFAR射电源提供光谱，每个光谱都提供一种宇宙指纹。WEAVE-LOFAR的观测将提供精确的距离信息，并使测量基本的物理特性成为可能，否则是不可能获得的，比如SMBH的质量或其宿主星系的恒星形成和化学特性。如果我们要研究SMBH种群的全部多样性，并发现最罕见和最极端的来源——那些真正考验我们理解极限的来源，这些数据集组合提供的大量样本是必不可少的。

At the heart of every massive galaxy in the Universe lies a super-massive black hole (SMBH), some with as much mass as 10 billion Suns crammed into a volume similar to our own solar-system. When these SMBH grow by eating matter from their surroundings, huge amounts of energy are released - making them the most extreme and energetic objects in our Universe. In addition to being fascinating objects in their own right, these SMBH are also believed to play an important role in the evolution of their host galaxies. If we want to completely understand how galaxies such as our own Milky Way came to be, we must therefore also understand the formation and evolution of their central SMBH. In recent years, observational studies have been able explore SMBH formation increasingly far back in cosmic history, revealing surprisingly massive SMBH that were able form in just the first 5% of the current age of the Universe. Crucially however, our understanding of these monsters in the early Universe is limited to only the very brightest optical sources - we are seeing only the tip of the iceberg. The goal of my research program is to build a complete picture of the early stages of SMBH formation - answering the questions of how, when and where the most extreme objects in our Universe were formed. My research will use an extensive new radio sky survey from the pan-European radio telescope, the Low Frequency Array (LOFAR), to study actively growing black holes, or Active Galactic Nuclei (AGN), throughout cosmic history. The unique power of radio observations is that they can peer through the gas and dust that obscure other signs of black hole accretion, meaning that LOFAR is able to reveal AGN activity that has previously been hidden from us. The combination of LOFAR's sensitivity and observing speed means that it is now discovering an unprecedented sample of AGN in the first 3 billion years of the Universe - the period of cosmic history when the biggest and most extreme SMBH are thought to have formed. While LOFAR offers an enormous leap in our ability to discover AGN activity across cosmic history, there is crucial information about these AGN that cannot be learned from their radio emission alone. We must combine these data with other measurements across the electromagnetic spectrum in order to unlock their full potential. During my Ernest Rutherford Fellowship I will combine the radio imaging of LOFAR with a new generation of complementary astronomical surveys that will enable me to build up a complete statistical picture of how SMBH accretion activity evolved and how this relates to the formation of the host galaxies themselves.Key among these surveys is WEAVE-LOFAR, an extensive five year project to provide optical spectra for over a million LOFAR radio sources, with each of these spectra providing a kind of cosmic fingerprint. The WEAVE-LOFAR observations will provide precise distance information and enable measurements of fundamental physical properties that would otherwise be impossible to obtain, such as the mass of the SMBH or the star-formation and chemical properties of its host galaxy. The enormous samples provided by this combination of datasets are essential if we are to study the full diversity of the SMBH population and discover the rarest and most extreme sources - those which truly test the limits of our understanding.