The RAS - Blackwell Prize 2000
The Michael Penston Astronomy Prize 2000
In my thesis, carried out at the University of Durham (UK), I applied a state-of-the-art model of galaxy formation and very large numerical simulations of dark-matter to the problem of galaxy clustering and demonstrated that the dependence of galaxy formation efficiency on dark-matter halo mass leads to a scale-dependent bias in the distribution of galaxies relative to the distribution of mass. Remarkably, this results in a correlation function in a flat, Omega_0=0.3, CDM model that is close to a power-law over four orders of magnitude in amplitude and which agrees well with the correlation function of galaxies measured in the APM survey. I also examined the reionization of the Universe by stars in high redshift galaxies and calculated the potentially observable signal of this process in the Cosmic Microwave Background. Finally, I made both theoretical and observational tests of some of the fundamental assumptions made in current models of galaxy formation.
I am currently working as a Prize Postdoctoral Scholar in Astrophysics at the California Institute of Technology (USA). In my present research I am pursuing further many of the techniques developed in my thesis. These include designing new statistical methods for quantifying galaxy clustering which are more physically intuitive, and therefore more useful, than traditional methods, and also constructing self-consistent models for the complex interactions between galaxy formation and the physics of the intergalactic medium which occur during reionization and which have significant consequences at the present day. I am also working in other areas, such as applying quantitative measures of galaxy morphology to large redshift surveys and calculating the properties of clusters expected to be detected in the near future by surveys in the Sunyaev-Zeldovich effect.
The prevailing theme of my thesis research at the Institute of Astronomy in Cambridge was to use the technique of quasar absorption line spectroscopy to probe the chemical evolution of galaxies and the intergalactic medium. By studying the elemental abundances in a population of intermediate redshift (z < 1.5) damped Lyman alpha systems (DLAs), I found that there is no evidence for significant metallicity evolution over many gigayears, contrary to what we would expect if these systems represent the bulk of star-forming galaxies. I therefore started a new survey for DLAs in order to determine whether our current samples are biased against metal-rich, but dusty, absorbers. Finally, I also investigated whether a significant amount of metals could be found in the IGM by looking at the lower column density absorption lines in the Lyman alpha forest.
I am now working as a post-doc at the European Southern Observatory in Chile. The survey that I started during my PhD is now complete, the main result being that any underestimate of DLA number density and gas content is at most a factor of a few. I am following up this survey to determine the metallicity of these DLAs, investigating their 21 cm absorption and inferring their dust properties from the optical and IR colours of the quasars. As a sideline, I am also involved in a new transit planet search, for which I am primarily dealing with radial velocity follow-up observations and also a program to study the connection between DLAs and gamma-ray burst host galaxies.
My thesis research at the University of Sussex and then the Open University concentrated upon Hubble Space Telescope observations of black holes in the Galaxy. The most compelling case for the existence of such black holes comes when they are in close binary stars. If a normal star comes close enough to the black hole then gas can flow from this star into an accretion disc around the black hole. This accumulates mass until the material drains into the black hole in a spectacular outburst when these objects can become among the brightest in the X-ray sky. My work used space-based ultraviolet, optical and X-ray observations to study the properties of the accretion disc and other components of the system during outbursts and attempt to understand how the outbursts occur.
My current research at the University of Southampton continues to be in the field of Galactic black holes. I am still actively involved in Hubble Space Telescope observations, and over the last two years we have obtained some of our most exciting results yet. Another important aspect of my postdoctoral work is to study black hole binaries when they are not in outburst and the disc is quietly accumulating material. These very dim objects may reveal evidence of the most fundamental property of a black hole: an event horizon within which even light is forever trapped. By studying variations in X-ray and optical light I hope to unravel the behaviour of material near the hole and determine if some gas does continue to disappear almost silently through the event horizon in between outbursts.
The Meteorology of Jupiter
("Equatorial and midlatitude circulation of Jupiter's atmosphere": D.Phil. thesis, 1999)
Jupiter has arguably the most interesting weather in the Solar System. Its most impressive features - the giant storms, high winds and cloud plumes - have been observed for centuries, but are still poorly understood.
My work involved modifying terrestrial weather-forecasting software to model Jupiter's atmosphere in unprecedented detail. By studying the creation, evolution and destruction of giant vortices in unstable jet streams I was able to infer the physical processes involved.
I also asked "Why does the wind blow from the west at Jupiter's equator?" A simple question; but the answer involves equatorial waves, low-frequency stratospheric temperature oscillations and some surprising filtering effects.
The Jupiter project was continued by a post-doctoral researcher. I turned my attention to Mars, working with colleagues in Oxford, Paris and Granada (Spain) on a Mars General Circulation Model and the European Mars Climate Database. This involved implementing and calibrating a parameterisation of radiative transfer in the upper atmosphere, and comparing results from the British and French models. The project is funded by the European Space Agency and aims (among other things) to improve the meteorological information available for planning spacecraft missions.
In late 1999 I left Oxford to join the Civil Service Fast Stream.
Obtaining reliable estimates of the intensity of the Earth's magnetic field through time is notoriously difficult. During my NERC funded PhD at the Geomagnetism Laboratory, Dept. Earth Science, Liverpool University, I helped in the development of a new palaeointensity technique in which high frequency microwaves are used to demagnetise and remagnetise palaeomagnetic samples. In particular, I developed the microwave palaeointensity technique for use with lava. During my research I carried out three palaeomagnetic studies using both conventional techniques and the new microwave palaeointensity technique. The studies were of historic lava from Mt. Etna Sicily, a detailed 'through the flow' study of the 1960 Kilauea lava flow, Hawaii and, a study of Tertiary Australian lava. My research demonstrated the viability of using the microwave palaeointensity technique with lava, and that the experimental success rate is much higher when compared to conventional techniques.
Since completing my PhD, I have stayed at the University of Liverpool in the Geomagnetism Laboratory. I am keen to continue using and developing the microwave palaeointensity technique, and at present Liverpool University houses the only operational machines in the world. My research has included investigating samples of Martian meteorites. For seven months I held a temporary lecturer position in the Dept of Earth Science teaching geophysics. From May 2001 I started a 3 year NERC funded postdoctoral position using the microwave palaeointensity technique to investigate magnetic field intensity behaviour through three successive field reversals found in a lava sequence on Hawaii.
I obtained my PhD titled "The significance of salt anisotropy in seismic exploration" from the School of Earth Sciences, University of Leeds under the supervision of Dr Michael Kendall. The thesis investigates the potential for seismic anisotropy in salt structures resulting from the preferential alignment of crystals during deformation. The work linked studies of texture development, elastic properties, forward modelling and seismic data analysis to provide a broad view of salt anisotropy from its development to its seismic implications and measurement in seismic data. Significant seismic anisotropy in salt bodies was predicted and subsequently measured, this contradicts the long held assumptions in the oil industry that salt bodies are isotropic and homogeneous. The thesis also involved further development and implementation of Maslov theory to provide improved synthetic seismograms in the presence of caustics where asymptotic ray theory breaks down. My PhD included a summer placements with both Schlumberger Cambridge Research and Amoco in Houston.
I am now working for ABB Offshore Systems Limited as a geophysicist in the Reservoir Geoscience group based near Penryn in Cornwall. We provide comprehensive microseismic monitoring and analysis services to the hydrocarbon and geothermal industry for monitoring reservoir subsidence, water/gas injections and hydrofrac operations. Seismic sensors placed in boreholes are used to record micro-earthquakes that occur in the reservoir, typically ranging in magnitude from 2 to -6. These events can provide much information about the reservoir including stress, location of active faults and fracture orientations. I am involved in many aspects of the microseismic work including research, software development, feasibility studies, network design studies and data processing and interpretation. ABB Offshore Systems is a part of the Oil, Gas and Petrochemicals Division of the ABB group that is a global engineering and technology company whose other core businesses include power and automation technology products, process industries, manufacturing and consumer industries, utilities and financial services. ABB has 160,000 employees in more than 100 countries.