Research in astrophysics and cosmology at the University of Bristol

This proposal is for a grant to researchers in the HH Wills Physics Laboratory of the University of Bristol to investigate important questions in astrophysics and cosmology.

Much cosmology over the past few years has been based on investigations of clusters of galaxies, and the first project is to ensure the usefulness of clusters by making reliable measurements of their masses. This involves statistically rigorous investigations using several methods on samples of clusters derived from X-ray surveys. The clusters span a wide mass range and are seen over half the age of the Universe, so we also have to take into account how clusters change in time. The X-rays come from hot gas atmospheres held by the clusters - though low in density these atmospheres account for much of the mass of normal matter, and have other detectable effects, for example on the microwave background radiation. Cross-checks with non-X-ray techniques of mass measurement will ensure the reliability of our results.

On a smaller scale, we know that individual galaxies also change in time, but there is currently little understanding of how these changes depend on galaxy mass and environment: galaxies of different masses change at different rates, for example. How these processes act with and against one another to build the population of galaxies that we see today is unclear, but the multi-band optical data that we have accumulated allows tests of how galaxies change, and how star formation is fuelled, in the low-redshift Universe. At higher redshift we will look for proto-clusters, which contain the fastest-evolving galaxies, to understand how galaxies evolve during the early growth of the first massive structures.

Essentially all massive galaxies contain massive black holes at, or near, their centres, and a third project will investigate how such black holes are able to create intense central radiation sources, and will use the changing brightness and spectrum of X-rays from the inner parts of these systems to study black hole physics and the gas held close to the black hole.

A fourth project looks at how the tiny regions in the centres of individual galaxies, near the central black holes, can affect gas on the large scale - by stopping catastrophic cooling of the atmospheres of clusters of galaxies, and by gradually making cluster atmospheres more magnetic over cosmic time. It is widely believed that a feedback process, in which gas in clusters is reheated by the ejection of very hot, fast, gas from the regions near black holes is involved, at least in one heating mode. Our calculations have identified the population of sources responsible for this heating, and now want to understand how the process works for these objects.

The fifth project involves the maintenance and improvement of codes used to work with catalogues of astronomical objects. These codes are essential when dealing with modern astronomical data, and are used world-wide, so are of great importance to many astronomers, but require development to deal with the increasing size and complexity of astronomical data. Some of the codes have even found their way into public products like the Microsoft World-Wide Telescope, and others are finding creative uses beyond astronomy.

The final project is theoretical, and investigates the nature of the gas/dust disks around young stars in which planets form. As young pieces of planets collide and assemble into larger planets they can also destroy one another. Some of the dusty disks we see around young stars may show evidence of this destructive side of planet formation. The purpose of the high-performance computer calculations to be done in this project is to interpret the extreme examples of dusty disks to see if they are changing because of giant impacts between young planets. The results from the calculations will be compared with continuing observations of changing disk emission.

Direct beneficiaries from the research will be our academic colleagues and interested members of the public, who will be exposed to the research results through our lectures, talks in schools, podcasts, press releases, WWW pages, appearances on radio and TV, and exhibits in and around Bristol. More indirectly, the public may be affected by advice given to local MPs or City Councillors (such as Mark Wright, who did a PhD in the Astrophysics Group a few years ago).

Commercial benefits have already been had from the TOPCAT work (projects with Microsoft Research). Spin-offs from the Fourier Transform spectrometer constructed for the radio telescope have benefitted BEAM and AlphaData. Research associated with the study of variability in active galaxies (Section 5) has formed the basis of a commercial contract, and provides some support for algorithm development relevant to LSST and SKA, as well as being of commercial benefit. This led recently to the company being awarded two major contracts, ensuring a flow of income for the next five to ten years, and also providing work for a local SME with whom we work on commercial-quality coding of our algorithms.

More generically, the sophisticated image and time-series analysis techniques used in our research can be applied to many problems. We will continue to work with the Atomic Force Microscopy group in the University to improve their imaging (as in recent imaging of moving DNA molecules), and are exploring the application of our techniques to medical imaging through the Clinical Research and Imaging Centre of the University.

Finally, the major economic output of this work will continue to be trained PhDs and PDRAs who mostly go into non-academic areas for their later careers. These careers have included local Government, the defence and security sector, plasma fusion research, meteorology, teaching, and finance.