Institute for Astronomy

Active Galactic Nuclei PhD Projects

Research projects on offer in our Active Galactic Nuclei group.

Observing AGN feedback in action with new-generation spectroscopic surveys

Ken Duncan and Philip Best

One of the key predictions of modern simulations of galaxy evolution is that feedback from accreting black holes (or Active Galactic Nuclei; AGN) plays a crucial role in shaping the growth of galaxies. In particular, AGN that produce extended relativistic jets visible in the radio (known as 'radio-loud AGN') are believed to be key to shutting down star formation in the most massive galaxies. However, the details of exactly how feedback from radio jets impacts their host galaxies have remained elusive.

This project will combine data from the deepest-ever radio continuum surveys (the LOFAR and MeerKAT telescopes) with detailed spectroscopy from a new generation of optical facilities, including the brand-new WEAVE spectrograph on the William Herschel Telescope and the forthcoming 4MOST survey facility in Chile. Using these datasets, the student will build a more complete picture of jet activity in galaxies from the early Universe until now, while also linking this activity to the properties of the galaxies they live in through the detailed measurements enabled by the WEAVE-LOFAR and ORCHIDSS (4MOST) spectroscopic surveys led by Dr Duncan.

The student will have the opportunity to get hands-on experience in the analysis of large observational datasets, and in working in collaboration with teams that span Europe and the world. Depending on the student’s interests and experience, there are a number of specific directions the project can take, including more detailed studies of individual objects (with facilities such as JWST or ALMA) or in linking the observations with predictions from the galaxy formation simulations led by the IfA.

Extreme Quasar Variability

Andy Lawrence

Activity in quasars, and Active Galactic Nuclei (AGN) more generally, is thought to be due to accretion of gas onto supermassive black holes, but the process is poorly understood. One of the most striking properties of quasars is their variability at all wavelengths, which gives us a chance to probe physical size-scales that otherwise we couldn't possibly resolve. Normal variability is a few tens of percent, but more dramatic changes can happen - AGN that temporarily switch off, others that slowly flare up by an order of magnitude over years, and small galaxies with no apparent previous AGN that have outbursts lasting a few months then disappear. These phenomena are a very difficult challenge for standard theory, and may involve the tidal disruption of passing stars, accretion disc instabilities, and gravitational microlens magnification. We have established a database of light curves thirty years long for hundreds of thousands of quasars, and within the PhD timeframe expect to gather new data, including new transient alerts  from the Vera Rubin Observatory.

The project could go in one of several directions. (i) Following up new outbursts with spectroscopy, as part of the Europe-wide PESSTO project; (ii) Analysing the 30-year database looking for correlations in black hole mass, luminosity, redshift, and so on, and comparing to model predictions; (iii) Developing new models of outburst spectra using the CLOUDY photo-ionisation code.  

Some relevant group publications:

Homan et al 2022 "The long-term broad-line responsivity in MKN 110" MNRAS in press

Nicholl et al  2022 "Systematic light-curve modelling of TDEs: statistical differences between the spectroscopic classes" MNRAS 515, 5604

Short et al 2020 "The tidal disruption event AT 2018hyz - I. Double-peaked emission lines and a flat Balmer decrement" MNRAS 498, 4119. 

Lawrence 2018 "Quasar Viscosity Crisis", Nature Astronomy 2, 102.