The RAS - Blackwell Prize - 2003
The RAS Michael Penston Astronomy Prize (Sponsored by PPARC and Wiley)
(Thesis studies at the Astronomy Centre, University of Sussex)
My doctoral research, which was supervised by Professor Andrew Liddle, was concerned with the inflationary scenario at its interface with observations through the cosmic microwave background (CMB). We began by studying the predictions for the scalar power spectrum, the primary observable relating to inflation, for certain non- standard inflationary models.
We went on to compile the full second-order slow-roll expansion of the inflationary power spectrum, and made a comparison with an exact numerical solution in order to assess the accuracy of these predictions. We found that for a wide range of parameter space, the desired 1% accuracy could be attained, making them suitable for comparison with precision observations coming from the WMAP and Planck satellites.
Finally, in order to test our methods we made a comparison with the then available CMB anisotropy data coming from COBE, BOOMERANG, MAXIXA, DASI and VSA detectors, leading to constraints on the inflationary parameters including an upper limit on the contribution of tensor modes (gravitational waves) to the CMB spectrum.
I am currently working as an EU CMBNET young researcher in Professor Ruth Durrer's cosmology group in the Theoretical Physics Department of Geneva University, Switzerland. My recent work has been concerned with analysing the WMAP CMB anisotropy data and its implications for inflation. These observations mark a watershed for inflationary constraints, since it has been found that certain specific inflationary toy models are now on the verge of being ruled out. We've also studied an aspect of high-energy inflation models relating to the number of e-folds of inflationary expansion, which actually provides a useful constraint that can be exploited, along with the observational constraints. I've gained experience working with the now ubiquitous Markov-chain Monte-Carlo methods, which has awoken an interest in Bayesian methods for statistical inference. I'm working to refine current methods so that they can be confidently applied to the future datasets including data from Planck satellite.
My doctoral research took place at the University of Oxford, working with Prof Jasper Wall. We analyzed the NRAO VLA Sky Survey, which is a radio survey covering about 80 per cent of the sky. In particular we used this survey to measure galaxy clustering. Radio galaxies are located at great distances and are a powerful means of probing large-scale structure at high redshift. We also detected the faint imprint of the "cosmic velocity dipole" in the radio galaxy distribution. The velocity dipole is a tiny fluctuation in the surface density of galaxies caused by the Earth's motion through the cosmos. This result provided a nice confirmation of the underlying isotropy of the Universe.
I'm currently a post-doctoral research fellow at the University of New South Wales in Sydney, Australia. I'm helping to develop a new technique for measuring dark energy in the Universe. Dark energy is a mysterious substance which makes up 70 per cent of the Universe, and which causes the current Universal expansion to accelerate. We wish to probe dark energy using a precise measurement of galaxy clustering, which is achievable by next-generation galaxy redshift surveys. I'm also studying "E+A galaxies", a special type of galaxy which has just completed a burst of star formation. These galaxies yield valuable clues to the process of galaxy evolution.
My PhD research at the Institute of Astronomy, Cambridge University, was based upon the analysis of the 2dF Galaxy Redshift Survey. This ambitious project was a joint UK-Australian effort to map the distribution of galaxies in the `local' Universe in more detail, and over a larger region of the sky than ever before. In so doing it generated a sample that was 10 times the size of any previously assembled - comprising over 200,000 different galaxies.
My thesis focussed on several different aspects of this survey, but the underlying theme was always to do with how different `types' of galaxies behaved. In particular we defined a new way of parameterising the type of a galaxy and then used this to study the observational constraints we could then place on galaxy-formation and evolutionary scenarios.
I'm currently a Hubble Fellow at Lawrence Berkeley National Laboratory, Berkeley. My research is similar to that I performed during my PhD; however, I now work on a greater variety of data-sets (including two other extremely large galaxy redshift surveys being carried out in America), and have branched out into the detailed study of small sub-populations within these surveys.
As a Hubble fellow I have a large degree of freedom in determining my own research path, which provides a very valuable opportunity to establish myself as an independent researcher.
The work for my thesis was carried out at the British Antarctic Survey, Cambridge, United Kingdom. My thesis work involved the development of a new kinetic plasma simulation code in order to study electrical resistivity generated by electrostatic plasma waves in low density space plasmas. Traditional models of electrical resistivity require collisions between particles. However in tenuous space plasmas, there are rarely collisions between particles, and so we have to look to interactions between waves and particles to generate electrical resistivity. Electrical resistivity is an important mechanism for magnetic reconnection, whereby the geomagnetic field is connected to the interplanetary magnetic field. In this way solar wind plasma has direct access to the Earth's magnetosphere. As such, magnetic reconnection is a key energy transfer process in the solar-terrestrial system.
The plasma simulation code closely follows the interactions between electrostatic ion-acoustic waves and plasma particles (protons and electrons). I showed that previous analytical estimates of the resistivity due to these waves were up to three orders of magnitude too small. This result suggests that magnetic reconnection may be easier to achieve than previously thought, bringing the theoretical predictions of magnetic reconnection more in line with observations.
I am currently working as a Research Associate in the Space Plasma Physics group at the University of Alberta, Edmonton, Canada. My research again involves plasma simulation codes. I am now working on the problem of electron acceleration above the auroral oval in the Earth's magnetosphere. We know that auroral displays are generated when high energy electrons collide with oxygen atoms high up in the Earth's atmosphere. The electrons are guided down to the atmosphere by the geomagnetic field. However, the mechanisms which accelerate these electrons to such high energies are not well understood. In order to understand why auroral arcs form, we need to look more closely at these acceleration processes. I have developed a plasma simulation code which looks at electron acceleration due to shear Alfven waves - electromagnetic waves which travel along the geomagnetic field lines. We are currently working on comparisons between the predictions from this new simulation code and observational results from rocket and satellite experiments.