Supermassive Black-Holes in Formation and their Role in Galaxy Evolution

Our Universe contains billions of galaxies like our own Milky Way, each harbouring a supermassive black-hole at its centre. The biggest galaxies today weigh more than a trillion times the mass of our Sun with supermassive black-holes weighing the equivalent of a billion Suns. But how did these galaxies and black-holes get so big? The Universe is almost 14 billion years old but the major growth spurt of galaxies took place more than ten billion years ago. Theory predicts that this epoch in our Universe's history was characterized by violent collisions of small galaxies. These collisions compressed the gas in galaxies to form stars, the new stars provided fuel for the supermassive black-holes to feed on and the massive galaxies of today were assembled with enormous black-holes at their centres.

Despite this well-accepted picture of galaxy formation we still have not observed many of these processes happening, particularly during the very active period of growth in our Universe's history more than 10 billion years ago. We want to catch the most massive galaxies and supermassive black-holes as they are growing but these systems are very rare; looking for them is comparable to looking for a needle in a haystack! Not only do we need sophisticated telescopes that can scan the entire sky searching for these monster galaxies, they also need to be sensitive enough to detect light that has traveled billions of years from when the galaxies were first forming, to reach us today. This has only recently become possible and new digital cameras have been mounted on some of the largest telescopes in the world to provide sensitive images covering most of the sky. I am working on data from several of these new digital imaging surveys.

My research involves scanning the digital images to locate the most enormous galaxies in our Universe as they are undergoing a major growth spurt. I have already identified the first of these ultra-massive growing galaxies in the distant Universe. Through high-resolution imaging of these newly discovered galaxies, we will be able to observe the various physical processes going on within them and how the supermassive black-hole is affecting these processes.

Within our new digital images of the sky lurk even rarer systems such as the first galaxies and supermassive black-holes in our Universe dating back to when the Universe was only 500 million years old. We are now able to watch these galaxies as they begin to feed their supermassive black-hole for the first time on their journey to growing to the monster black-holes of today. Observing this first feeding phase is critical for building up an understanding of how supermassive black-holes grow.

Most digital imaging surveys detect starlight from galaxies in the visible portion of the electromagnetic spectrum. However, dust in galaxies can absorb visible light, which is then re-radiated at the longer infrared wavelengths. Infrared data therefore allows the most unbiased view of star formation in galaxies. Utilising new surveys that trace light at infrared wavelengths, my research will measure the number of stars being formed in distant galaxies with actively feeding supermassive black holes. The aim is to determine if the supermassive black-hole directly impacts the rate at which a galaxy is forming stars, therefore controlling how massive its host galaxy will eventually become.

Taken together my research aims to build up a coherent observational picture of the formation of massive galaxies and supermassive black-holes by directly observing them as they are being assembled in the early Universe. This will be done by bringing together new data from some of the largest astronomical surveys across the electromagnetic spectrum, that are currently underway.