The RAS Michael Penston Astronomy Prize 2002 (Sponsored by PPARC)
(Thesis studies at the School of Chemistry, University of Bristol)
My doctoral research consisted of analysis of observational data of the OH masers in the star-forming region W3(OH). The observation was performed with the VLBA in 1996 at very high resolution in both polarizations of all four ground state OH maser lines, and at the time was the best observational dataset ever recorded of that region of space. Maser emission is well fit by 2-dimensional elliptical Gaussians, which allows for high precision measurements of position, dimensions and flux of each maser. Much research time was spent developing software that could deal with the huge number of masers detected in the observation, and after that much time was spent analysing the masers, filtering out noise, finding Zeeman pairs, and developing a model of the region. The final model of the region - a disk of gas in Keplerian rotation about a star of 8 solar masses - were presented in the thesis.
Current work: Applying astrophysics to the commercial world is never easy, but the heavily computation nature of my research meant that I was well skilled in general computing, programming and IT. I joined British Telecom on their graduate course; fortunately just before the serious downturn that has recently hit the IT industry. Within BT I work for a company that develops IT based solutions for internal needs. I have been trained in Oracle PL/SQL development and programming, and was immediately placed on a high-profile project called "Self Motivated Teams", which is the development of a performance related pay scheme. This was originally designed for 20,000 engineers, but has been so successful in trials that it is now likely to be implemented throughout BT and may be sold internationally as well.
My doctoral research took place in the Physics & Astronomy Dept of Cardiff University in South Wales, under the supervision of Dr Stephen Eales. My thesis was in the field of submillimetre astronomy, studying the thermal emission from cool dust in galaxies. In 1997, at the start of my PhD, a revolutionary new instrument called SCUBA (Sub-millimetre Common User Bolometer Array) was commissioned on the James Clerk Maxwell Telescope located on Mauna Kea in Hawaii. SCUBA enabled astronomers to take images of the sky at wavelengths between 350-850 microns, with much better resolution and at much higher speed than had been possible before. Many groups began deep surveys of small regions of sky in order to search for primeval elliptical galaxies. These are galaxies forming almost all of their stars in one huge burst, and were believed to be enshrouded in dust and therefore invisible to even the largest optical telescopes. At submillimetre wavelengths, however, these objects would be very luminous due to the large quantities of dust, and many such high redshift submillimetre sources were discovered. While I am involved in one of the deep surveys (the Canada-UK Deep Submillimetre Survey), my PhD project was to make the first measurements of the submillimetre properties of LOCAL galaxies - the SCUBA Local Universe Galaxy Survey (SLUGS). This was an essential step in order to be able to interpret the observations of the distant universe. I observed nearly 200 nearby galaxies with SCUBA and produced the first direct estimate of the submillimetre luminosity and dust mass functions (how the space density of galaxies depends on luminosity and dust mass). I also investigated the temperature of the dust in objects of different types and how the dust related to other properties, such as optical luminosity, gas mass and radio power.
Current research: Since completing my PhD I was awarded a PPARC post-doctoral fellowship, for which I remained at Cardiff. I am now 2 years into this 3 year post.
I have been extending the work on the SCUBA local universe survey to samples selected in different ways (such as optically selected galaxies). In particular I found that most of the dust mass in galaxies is often at rather cold temperatures (15-20 K). While COBE showed this to be the case for the Milky Way, it was not certain that more FIR luminous galaxies also contained dust this cold. I am interested in linking what we know about local galaxies in the FIR/ submillimetre with the distant populations discovered by SCUBA. Using what we know about dust in galaxies from the local survey, I produced an estimate of the dust mass function for the high redshift (z=2-3) submillimetre selected sources found in the deep SCUBA surveys. Combining this with simple chemical evolution models showed that most of the metals at high redshift reside in the I also try to provide observational constraints to chemical evolution models, observing dust in low metallicity dwarf galaxies and looking for dust in young supernova remnants helps to pinpoint the sources of dust in the ISM and enables us to place limits of how quickly dust can form in high redshift galaxies.
Thesis research: Numerical Methods for Gravitational Lensing.
Within the framework of Einstein's theory of gravitation, all matter deflects light. On cosmological scales, this may lead to distortion, magnification and multiple imaging of light sources located behind massive structures, like galaxies or clusters of galaxies. The effect is in some ways analogous to optical lenses. In my thesis work, carried out at the Cavendish Laboratory, Cambridge, between 1997 and 2000, I developed, described and applied numerical methods that predict the effect of various realistic mass distributions on the images of background sources. In my thesis I showed how, upon comparing these predictions with properties of observed gravitational lenses, one may constrain the mass distribution in different lens systems, thus providing a unique way to probe and find the enigmatic "Dark Matter" on various scales, from galaxies to clusters of galaxies.
Current research: My current research at the Kapteyn Institute in Groningen, Netherlands involves both "strong gravitational lensing", when the mass distributions are compact enough to form multiple images of background sources, and "weak gravitational lensing", where more extended, less concentrated mass distributions lead only to slight distortions of the background light. In the strong lensing regime, I apply and extend the methods developed during my PhD to study new realistic models of the mass distributions in galaxies, in particular massive, early-type galaxies. In the weak lensing regime, I am currently implementing different methods that enable the reconstruction of the dark matter distribution from its distortion of background galaxies. When applied to high quality images that are to be obtained using new wide field CCD cameras, these methods will make it possible to obtain maps of the dark matter distribution with unprecedented accuracy.
My PhD was completed in the Radio and Space Plasma Physics group at the University of Leicester, with the supervision of Prof. Stan Cowley.
My thesis work was an investigation of the jovian magnetosphere, mainly through the interpretation of magnetometer data from a variety of interplanetary spacecraft (Pioneer-10, Pioneer-11, Voyager-1, Voyager-2, and Ulysses) and from the Galileo orbiter. The principal interaction between a planet and its plasma environment is mediated by the magnetic field, therefore investigations of the magnetic field configuration provide significant information about the dynamics of the system. Studies for my thesis centred on the large-scale azimuthal and radial current systems present within the jovian magnetosphere. The azimuthal current system inflates the magnetic field and produces an inwardly directed force, which opposes and balances the outward force of the plasma inertial and pressure forces. The main source of the plasma is the volcanically active moon Io. My work showed that a local time asymmetry exists in the azimuthal current, such that at a given radial distance, the current is twice as strong on the nightside than on the dayside. This is interpreted as being due to the asymmetrical confining effect of the solar wind flow on the magnetosphere. The radial current system is associated with the bending of the magnetic flux tubes out of meridian planes and is principally caused by the transmission of angular momentum from the rapidly spinning atmosphere to the equatorially confined plasma. This large-scale current system consists of the equatorial radial current, field-aligned currents (FACs) flowing into or out of the equatorial plane, and is closed via Pedersen currents flowing in the conducting layer of the jovian ionosphere. This paper for the first time calculated the divergence of the total equatorial current (contributed to by the two current systems mentioned above) and has led to the understanding that the main auroral oval at Jupiter is produced by the upward FACs in this system.
Current research: After a period of maternity leave, I am now a Research Associate (in the RSPP group at Leicester). More recently my studies have extended to the kronian magnetosphere (as well as continuing studies of the jovian system), with a view to preparing for Cassini's arrival at Saturn in 2004. We have been looking at the magnetic field and plasma data from the Pioneer-11, Voyager-1 and Voyager-2 fly-bys, the only spacecraft to have visited the planet thus far. We have recently looked more closely at the Pioneer-11 perturbation fields (having subtracted the field due to internal origins) and have identified that an azimuthal ring current exists at this time which is similar to that identified and modelled during the Voyager fly-bys. The ring current during this fly-by is distributed over a similar volume, but lies closer to the planet. This is most likely due to the more compressed nature of the system during the Pioneer fly-by. We calculate the azimuthal magnetic fields expected to be present in Saturn's magnetosphere associated with two physical effects, and compare them with the fields observed during the fly-bys of the two Voyager spacecraft.
The first effect is associated with the magnetosphere-ionosphere coupling currents which result from sub-corotation of the magnetospheric plasma. This is calculated from empirical models of the plasma flow and magnetic field based on Voyager data, with the effective Pedersen conductivity of Saturn's ionosphere being treated as an essentially free parameter. This mechanism results in a 'lagging' field configuration at all local times. The second effect is due to the day-night asymmetric confinement of the magnetosphere by the solar wind (i.e. the magnetopause and tail current system), which we have estimated empirically by scaling a model of the Earth's magnetosphere to Saturn. This effect produces 'leading' fields in the dusk magnetosphere, and 'lagging' fields at dawn. Our results show that the azimuthal fields observed in the inner regions can be reasonably well accounted for by plasma sub-corotation, given a value of the effective ionospheric Pedersen conductivity of ~1-2 mho. We have also established, from theoretical considerations, that the aurora at Saturn is not produced by plasma sub-corotation, as at Jupiter, and postulate that the aurora is more likely to be driven externally by the solar wind-magnetosphere interaction (akin to the situation at Earth).
Deformation of the earth's crust results in faults, which are the locus of earthquakes and potentially act as conduits or barriers to flow through rocks. Studies of fault networks in continental crust have revealed that the distribution of fault sizes often follows a power law. This raises the question "Can power-law distributions be extrapolated, either to smaller length scales or wider areas?" My research at the University of Edinburgh, under the supervision of Patience Cowie and Ian Main, sought to establish a quantitative physical basis for identifying and discriminating between the geological factors that control the distribution of sizes in fault populations. By combining fieldwork in the Chimney Rock Fault Array, Utah, and numerical modelling, I was able to show that fault size distributions are controlled by fault growth processes, which in turn depend on the initial and boundary conditions of the system. Systematic changes due to fault growth processes can, however, be masked by the effects of heterogeneity. This suggests that extrapolating power law scaling from one area to an adjacent area is inadvisable, even if the areas contain the same rock types and deformation histories. Moreover, numerical modelling showed that power law size scaling may breakdown at high strains. This suggests that extrapolating power laws for size scaling beyond the range of observation may be inappropriate in high strain regions.
Current Research: Since completing my thesis, I've been working for Shell U.K. Exploration and Production as a geoscientist where I continue to consider the effects of faults on fluid flow, and the issue of fault size scaling.
During my DPhil I worked in the sub-department of Atmospheric, Oceanic and Planetary Physics at the University of Oxford, my research topic being the simulation of Martian dust storms. This involved constructing a dust transport scheme within an existing computer model of the Martian atmosphere. By parameterizing the lifting of surface dust, and allowing this dust to affect atmospheric temperatures, the model is able to simulate the growth, onset and decay of several types of dust storm, and their atmospheric impact, in a self-consistent manner. In particular, some storms closely resemble those which have been observed in the Hellas and Chryse regions on Mars.
Current research: I am still at Oxford, but am now working on several Mars-based projects. The first is to improve the simulation of dust storms, particularly by attempting to increase interannual variability in the type of storm produced spontaneously within the model at different times of year, which is currently substantially less than that observed. I am also looking at the use of 'breeding vectors' to determine modes of instability and predictability in the modelled Martian atmosphere. Finally, I am using the model with altered planetary orbital characteristics (such as obliquity) to simulate the atmospheric circulation and dust transport during past epochs.