The Roles of the Mid-infrared and Surveys in The Life and Times of Quasars

Black holes are intriguing objects. These regions of the Universe where mass is so dense, and gravity so strong, that even light cannot escape, were once thought mere oddities due to their extreme properties. Today, however, black holes are now thought to be vital in the formation and lives of galaxies, including our own Milky Way.

Observations, including those from the Hubble Space Telescope, have discovered black holes with masses a million or more times that of the Sun lurking at the centres of nearby galaxies. However, upon analysing these data further, there are two very surprising findings. First, these aptly named "Supermassive Black Holes" are ubiquitous at the centres of galaxies, and second, there is a relationship between the mass of the black hole and the properties of the galaxy.

Thus, the question arises, do black holes have an intimate relationship with their host galaxy? Do they inform, limit and influence how a galaxy - including its constituent stars and gas - forms and evolves? One possible line of evidence supporting the idea that black holes "regulate" their host galaxies is when one considers the energy liberated by mass falling into the black holes potential well.

As gas and dust fall towards a black hole, but before it gets "swallowed", an accretion disk can form which swirls around the black hole, feeding it. However, due to the intense gravitational fields, the large amounts of angular momentum, and friction between the infalling layers of gas, the accretion disk can heat-up to tremendous temperatures, in the process emitting optical, ultra-violet and X-ray light. If a supermassive black hole at the centre of a galaxy is actively accreting, then this "active galactic nucleus" is termed a quasar.

The broad aim of my research is to discover and study quasars; to find out how they are fueled, how they generate their energy and how they can influence the host galaxies they live in.

I use several telescopes across a range of wavelengths, including data from the Sloan Digital Sky Survey and the Hubble Space Telescope in the optical, and the Spitzer Space Telescope and the WISE satellite in the infrared. The infrared is important since quasars emit a considerable amount of their energy at these wavelengths, and one goal is to make sure we account fully for the entire energy production from supermassive black holes.

It is with the data from these great observatories that I will discover and examine quasars, test theoretical and computer models of how quasars are fueled, and gain new insights into how the galaxy-quasar symbiosis is achieved.

This research has potential impact and wider benefits to society in two flavours. First, the direct technological spin-offs that are associated with e.g. space-based telescopes and detector technology. Second, and less tangible, but more importantly, this type of research, keeps the "awe" factor high. And it is this resource, from which "improving natural knowledge" subsequently flows.