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Student Projects in the Theory Group for 2007

The following Threory Group research projects are available for PhD research students starting in 2007.

If you are interested in disussing these or similar project ideas then please contact the relevant project supervisor. You can find their contact details from the Staff Directory.

Project Title:

Galaxy formation and evolution

Supervisor: Prof. Shude Mao

The formation and evolution of galaxies is one of the most exciting topics in astrophysics. Many fundamental issues in this area still need to be understood. e.g., How is the Hubble sequence formed? How does it evolve as a function of time?

Theoretical PhD projects will involve hydro-dynamical simulations and comparisons with observational data (e.g., from the SLOAN Digital Sky Survey). The projects will use the COBRA linux cluster at JBO and other places. Possible topics include:

1) The evolution of hot and cold gas in galaxy mergers and their effect on the formation and growth of active galactic nulei.

2) The evolution of bars in cosmological simulations to explore the effect of gas and substructures in galaxies.

3) The effect of substructures on astrometry in gravitational lenses.

PhD candidates interested in this project are encouraged to contact me via email (smao@jb.man.ac.uk) or drop by my office to further discuss potential projects.

References: Mo H.J., Mao, S., and White S.D.M. 1998, MNRAS, 295, 319

Can low resolution HI observations at intermediate redshifts probe cosmology?

Supervisors: Dr R.A. Battye & Dr R.D. Davies

Neutral hydrogen (HI) in the IGM of spiral galaxies in the local universe has been observed using the flip-flop transition between two hyperfine states of hydrogen which emits EM radiation with wavelength 21cm. At present the highest redshift detection of HI is at z=0.18, but a number of observational projects are underway to make detections at much higher redshifts. In particular, the Square-Kilometre Array (SKA) which could find $10^9$ galaxies over a wide redshift range.

The SKA is unlikely to be even partially operational before 2015, but a number of pilot projects are currently being proposed to test various respect of the SKA technology. These instruments are only likely to have moderate resolutions and sensitivity compared to the SKA, and it is unlikely that they will be capable of making significant HI surveys for individual galaxies.

It has been proposed that it might be possible to detect much larger objects such as clusters via the combined effect of using these instruments, but no such detection has yet been made. If detections of large numbers of clusters are possible at high redshifts it should be possible to significantly constrain the evolution of the neutral component of the universe and cosmological parameters.

The aim of this project is to assess the feasibility of this idea by performing observations and making improved theoretical calculations. The initial aim would be to be half observations, half theory, but this can be negotiated according to the taste of the student. Preliminary observations using the Lovell telescope have been made, but the noise level is not sufficiently low to make a detection at present. Further observations are planned using the Lovell, as well the Green Bank Telescope and the Very Large Array in the US, and the Giant Metre-wave Radio Telescope in India.

Non-gravitational heating in galaxy clusters

Supervisors: Dr R.A. Battye & Dr T.J. O'Brien

Galaxy clusters are the largest virialized objects in the Universe and can weigh as much as $10^{15}$ solar masses. Due to the enormous gravitational potential the gas in the centre of the cluster can be heated to temperatures in excess of $10^{7}$K. This gas emits X-rays via thermal Bremsstrahlung and can also create significant distortions in the cosmic microwave background via the Sunyaev-Zel'dovich (SZ) effect. A considerable number of observational programs are underway to detect large (approx 10000) cluster samples using both these effects.

Under the assumption that the gas in the cluster is adiabatic all the properties of the gas can be computed and this is a common approximation used when making predictions of the number of clusters that will be found in X-ray and SZ effect. However, observations of local X-ray clusters indicate that this is not the case, suggesting the possibility of non-gravitational heating, presumably due to feedback from AGNs and supernovae.

The aim of this project is to model the effects of AGNs with numerical simulations using our own codes and the freely available hydrocode FLASH which was originally written to model thermonuclear explosions in supernovae. It will involve placing AGNs with a duty cycle as predicted by observations in an initially adiabatic cluster to determine the extent to which this affects the relationship between the mass and temperature of the cluster and the profile of the gas. The eventual aim of the project is to produce calibrated scaling relations between the cluster properties which can be used to make improved estimates of the yield of X-ray and SZ observations.

The Cosmic Microwave Background

Supervisors: Richard Battye, Ian Browne, Richard Davis, Rod Davies, Patrick Leahy, Althea Wilkinson, Peter Wilkinson

See PhD (and MSc) projects with the Cosmic Microwave Background group.

Hydrodynamic Simulations of Galaxy Clusters

Supervisor: Dr Scott Kay

Clusters of galaxies continue to be routinely used to measure cosmological parameters such as the amount of dark matter and dark energy in the Universe. Central to these measurements is that we understand the relationship between the luminous (stars and hot gas) and dominant dark matter components. It is now firmly established that supernovae and AGN-powered outflows play a crucial role in establishing this relationship, but the physics is still poorly understood.

Hydrodynamic simulations of galaxy clusters allow us to study these objects in a self-consistent manner. They are particularly useful in that they provide us with an important resource with which to assess the effects and relative importance of various physical processes. In this project, the main task will be for the student to incorporate a new model for the effects of supernovae and AGN outflows within state-of-the-art cluster simulations. By comparing to the high-quality observational data that is becoming available, the aim will be to produce the most realistic models of galaxy clusters to date. The models can then also be used to investigate the reliability of clusters as cosmological probes.

Note this project is heavily computational and will involve a lot of programming (likely in C), the use of parallel supercomputers and numerical analysis of large datasets (in C and IDL). It therefore requires a student with a strong aptitude in this domain.

Measuring Evolution in the X-ray Luminosity-Temperature Relation of Galaxy Clusters

Supervisor: Dr Scott Kay

It is well known that the X-ray luminosity and temperature of the hot gas in clusters in the low redshift Universe are well correlated, forming the Luminosity-Temperature (or L-T) relation. A new survey, called the XMM Cluster Survey (or XCS), is now underway to measure the relation for distant clusters to determine how much the L-T relation evolves with redshift. This measurement is particularly crucial for cosmological studies using clusters, but also reveals information on the galaxy formation processes which affected the intracluster gas.

The aim of this project will be to apply newly-developed codes by French collaborators to construct mock X-ray cluster catalogues (from both models and simulations), as would be observed with the XMM X-ray satellite. These clusters can then be processed using X-ray observer's software to determine their luminosity and temperature. The reliability of measuring evolution in the L-T relation from these mock catalogues will be assessed and its impact on cosmological parameter estimations investigated.

The project will involve collaboration with the XCS team, mainly based in the UK, and collaborators in Paris and Toulouse. It will also require a significant amount of computing using the C and IDL languages.

Microlensing

Suprevisors: Prof. Shude Mao & Dr. Eamonn Kerins

At Jodrell we have a very active group involved in microlensing research, with close collaborations with scientists elsewhere (such as Cambridge and Warsaw). There are usually several PhD projects, both observational and theoretical, on gravitational microlensing. Some examples are illustrated below.

A PhD student is sought to reduce the 300Gbyte of data from the world-leading microlensing observing team, the Optical Gravitational Lensing Experiment (OGLE). The student will improve the existing difference imaging analysis pipeline, and produce optical depths for single and binary microlensing events in about ten fields towards the Galactic centre. The results will then be used to constrain the inner structure of the Milky Way.

Microlensing data has also produced many excellent colour-magnitude diagrams for many fields toward the Galactic centre. So far these have not been explored fully to understand the stellar populations (such as their metallicity and age distributions) and the Galactic structure toward the Galactic centre. A student with interests and prior experience in stellar populations will be richly rewarded in pursuing research in this area.

Prior experience of optical data reduction experience and familiarity with IRAF will be desirable, although not essential. C (or equivalent computer language) programming skills are an essential requirement.

Some more information about microlensing activities can be found here.

 
Last updated 08 Apr 2008