Revealing the hidden early lives of super-massive black holes

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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.