Potential PhD projects: Extragalactic Astrophysics and Cosmology

Project: The evolution of galaxies in emerging large scale structures

Supervisor: Dr Sean McGee

Galaxy clusters are extraordinarily valuable as laboratories for a wide range of tests and experiments. In particular, observations of the infall and transformation of satellite galaxies within clusters allow us to directly tie our understanding of cosmology to our knowledge of galaxy formation. The first galaxy clusters emerge from the initial density perturbations within the early Universe and become virialized at redshifts between 1 and 3. Interestingly, this is also the epoch of galaxy formation, when star formation and AGN activity peaked. The goal of this project is to observe what happens when these rapidly forming galaxies are dropped into the extreme environment of galaxy clusters, which will have implications for our understanding of galaxy formation, feedback and the baryon cycle of galaxies.

We have been recently allocated a large amount of telescope time on the Gemini telescopes in Hawaii and Chile as part of the GoGreen project. The student will join this international collaboration and play a key role in the exploitation of this and other supporting data. The timing of the project is well suited for the length of a PhD, with several high impact results resulting on this time frame. Opportunities exist for observing on several large telescope throughout the project.

For more information, please email Dr. Sean McGee (smcgee[at]star.sr.bham.ac.uk)

Project: Probing the early universe with extremely low metallicity stars

Supervisor: Dr Sean McGee

Understanding how the first generation of stars emerged in the early Universe is a major frontier in astrophysics. While direct observations are not possible with current facilities, the detailed study of stars in nearby dwarf galaxies is beginning to allow us to infer the physics responsible for the first stars. In particular, extremely metal poor stars, thought to have formed from nearly pristine gas in the early Universe, are sensitive probes of the formation of the first stars and their subsequent chemical pollution of the environment. Measuring detailed elemental abundances in the spectra of these stars can be used to infer the typical masses and supernovae energetics of the first stars in the Universe.

Dwarf galaxies are the ideal places to look for such low metallicity stars because of their age, size and proximity. Besides the first generation of stars, the results of these studies will have implications for cosmic reionization, the early chemical enrichment of the Universe and the evolution of dwarf galaxies. Either observationally or theoretically focussed projects are possible, as well as some combination of the two.

For more information, please email Dr. Sean McGee (smcgee[at]star.sr.bham.ac.uk)

Project: Cosmology from gravitational lensing observations of galaxy clusters

Supervisor: Dr Graham P. Smith

The mass, shape, internal structure, and matter content (both luminous matter and dark matter) of galaxy clusters are all sensitive to the details of our cosmological model. This is due, in large part, to the privileged position of galaxy clusters at the top of the "cosmic food chain" - i.e. they are the most massive objects in the universe, in which massive structures such as galaxy clusters grow hierarchically by ingesting smaller systems. Despite major progress in recent years on measurements of cosmological parameters, there remain many exciting open cosmological questions, relating to (for example) the existence/properties of "dark matter" and "dark energy", the validity of General Relativity on cosmological scales, and the spectrum of initial density fluctuations in the early universe. As the Principal Investigator on the Local Cluster Substructure Survey (LoCuSS), Dr Smith has assembled an unprecedented wealth of data with which to probe the mass and internal structure of galaxy clusters, including sensitive gravitational lensing observations from the Subaru Observatory and Hubble Space Telescope, and complementary data at infrared, X-ray, and millimetre wavelengths. An opportunity therefore exists for a student with cosmological interests to work with Dr Smith on the cosmological exploitation of the LoCuSS dataset, exploring the topics outlined above and/or new ideas that emerge during the timespan of the PhD.

For more information please look up Dr Graham P Smith's webpage
or e-mail him (gps[at]star.sr.bham.ac.uk).

Testing gravitational lensing measurements of galaxy clusters

Supervisor: Dr Graham P. Smith

The astrophysics and cosmology community is investing heavily in several surveys that aim to measure the dark energy equation of state parameter (w=rho/P) using galaxy clusters, to per cent level precision. These surveys represent one of four independent probes, the others being type Ia supernovae (SNIa), baryon acoustic oscillations (BAO), and cosmic shear. The success of cluster-based dark energy experiments, just like the other methods, will depend on the precision to which systematic errors can be identified, controlled, and (preferably) eliminated. In a nutshell, cluster cosmology depends on being able to measure the mass of galaxy clusters reliably. In principle the tool of choice for measuring galaxy cluster mass is gravitational lensing (the deflection of light by mass), however the reliability of lensing- based mass measurements has yet to be tested to the levels required by dark energy experiments. Dr Smith's group are playing a leading role in the global effort to test the reliability of lensing-based measurements of cluster mass, via his leadership of both the Local Cluster Substructure Survey (LoCuSS), and the mass measurement working group of the upcoming Ultimate XMM Extragalactic Survey (XXL). An opportunity exists for a student to join Dr Smith's team to work on stringent tests of lensing-based mass measurement methods using both real observational data from Subaru Observatory, and also from synthetic observations of simulated clusters. The results from this thesis will contribute directly to the success of LoCuSS, and XXL, and will also help to define the state of the art methods upon which other cosmological surveys will depend.

For more information please look up Dr Graham P Smith's webpage
or e-mail him (gps[at]star.sr.bham.ac.uk).

Project: Pan-chromatic Study of Galaxies and their Environment

Supervisors: Dr Graham P. Smith and Dr Felicia Ziparo

According to the hierarchical growth of structure formation, galaxies experience a wide range of environments throughout their lives, from the low-density "field" regions to dense regions in the cores of galaxy groups and clusters. It is well known that the properties of galaxies are related to their environment, suggesting that environment plays a role in galaxy evolution. However the physical processes responsible for transforming gas rich star-forming galaxies into gas poor early type galaxies, and the role of these processes as a function of environment remains a controversial and hotly debated topic. Dr Smith's group, and collaborators in Arizona, Japan, Finland, and Chile, have assembled a superb dataset with which to tackle this problem, as part of the Local Cluster Substructure Survey. The data include ultraviolet, optical, and infrared imaging with GALEX, Subaru, and ESA's Herschel Space Observatory, plus optical spectroscopy from ESO's VLT. An opportunity exists for a student to join the group to use these data to investigate galaxy evolution in field, group, and cluster environments. Example projects include (1) integral field spectroscopy of galaxies in groups falling into clusters, and (2) comparing optical, ultraviolet, and infrared indicators of star formation.

For more information please contact Dr. Graham Smith (gps[at]star.sr.bham.ac.uk) or Dr. Felicia Ziparo (fziparo[at]star.sr.bham.ac.uk).