Research Summary

My research focuses on modelling the formation and evolution of galaxies. The primary aim of my research program is to develop a detailed and, most importantly, quantitative model of galaxy formation based upon known physical laws rather than empirical rules. Our empirical knowledge of galaxy formation is rapidly becoming quantitatively precise, and so has the potential to strongly discriminate between theoretical ideas regarding the formation and evolution of galaxies. Unfortunately, the required confrontation of theory with observations cannot occur at present as our ability to analytically model galaxy formation is currently restricted to making predictions accurate only to within "factors of a few." Progress can only be made therefore by developing a model of galaxy formation which incorporates the relevant physics in detail and which strives to solve that physics to high accuracy. These goals require the use of state-of-the-art models of galaxy formation, both N-body and phenomenological (a.k.a. "semi-analytical"). Over the past ten years I have extensively developed and enhanced the semi-analytic model of galaxy formation, Galform, originally developed at the Institute for Computational Cosmology at the University of Durham. This is now arguably the most advanced and detailed analytic model of galaxy formation available.

Galaxy Formation at the Highest Redshifts

This is a simulated view of the far universe as seen through NASA's James Webb Space Telescope (JWST) and was used by NASA during earlier planning of the JWST (then NGST) project. The photograph shows a simulated 20-hour observation with JWST of a random patch of the sky, located far from the plane of our Milky Way, that is cluttered with stars. The simulation is based on result from an earlier implementation of the Galform semi-analytic model of galaxy formation. My current research is now revisiting this study as the launch of JWST draws ever closer.

Credit: NASA, Andrew Benson and the JWST Science Team (STScI).

Feedback from Active Galactic Nuclei

With Arif Babul, I am developing a more sophisticated model of black hole growth and jet production which is embedded within a hierarchically growing population of galaxies. As part of this work we have developed a relatively simple model to compute the rate of spin up (or down) of an accreting black hole and the power of the jets it produces while accreting. The figure shows the efficiency (measured relative to the accretion luminosity) of jets driven out of supermassive black hole plus accretion flow systems as a function of the spin (j) of the black hole. The jet efficiency is divided into contributions from winds driven from the accretion disk, and jets launched from close to the black hole horizon. Points show results from relativistic magnetohydrodynamics simulations, while the lines indicate the results from my model of jet efficiency. This model is simple to implement in analytic calculations but agrees extremely well with relativistic magneto-hydrodynamic calculations.