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:Topics at the interface of Cluster Astrophysics and Cosmology

Supervisor: Dr Sean McGee and Dr Graham P. Smith

Galaxy clusters are potentially the most powerful probe of dark energy and gravity theory on large scales (arXiv:1604.07626), and they are fundamental to many unsolved problems in astrophysics, including the transformation of galaxies and the baryon budget of dark matter halos as function of halo mass. The interface between cluster astrophysics and cosmology is therefore very rich with many exciting future opportunities from upcoming surveys, including LSST, JWST, Euclid, and SKA. There is an opportunity for a student to pursue one or more projects in this area, for example:

  • Diffuse intracluster light as a function of halo mass - the amount of diffuse star light in galaxy groups and clusters is a very controversial topic, with some authors claiming that groups (out of which we believe cluster to be built) to have higher stellar mass fractions than clusters, by virtue of their diffuse light. We have data in hand from telescopes such as Subaru with which this issue can be investigated in great detail to potentially lay this controversy to rest, at least at low redshift. Low surface brightness science (of which intracluster light is one example) will be a key science topic for LSST next decade, especially at high redshift.
  • Dwarf galaxies in clusters and selection of background galaxies for weak-lensing studies - identifying which of the faint galaxies observed along lines of sight through galaxy clusters are cluster members and which are background galaxies is very challenging, and of critical importance to astrophysics and cosmology communities alike. On the one hand measuring the numbers and understanding the physics of the faintest galaxies in clusters is a key test of contemporary theories of galaxy formation. On the other hand, eliminating the faint cluster galaxies from samples of weakly-lensed background galaxies is one of the biggest challenges in using clusters for cosmological studies. This project will use deep data from ESO's MUSE instrument and deep HST imaging data to conduct a joint study of faint cluster galaxies and methods for selecting background galaxies.
  • The key venue for exploring the physics of the assembly of large scale structure in the universe is the infall regions of massive galaxy clusters. Key open issues include whether galaxy groups falling in to clusters are different from isolated galaxy groups, and whether/how infalling groups affect the reliability with which the mass of galaxy clusters can be measured for cosmological experiments. We have a unique sample of 40 galaxy groups that are falling in to clusters at z=0.2, as part of the LoCuSS survey. Benefiting from a uniquely rich dataset that spans millimetre to X-ray wavelengths, this project will explore the transformation of galaxies in infalling groups including the issue of "pre-processing", and the scaling relations of infalling galaxy groups.

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

Project: Towards modelling the structure of galaxy clusters for the LSST era

Supervisors: Dr Will Farr and Dr Graham P. Smith

Next decade we will discover thousands of strong-lensing clusters across a broad range of redshifts with a combination of LSST and Euclid. One of the key challenges will be to infer the structure of these clusters and thus achieve robust constraints on the physics of galaxy clusters and how this physics impacts on our ability to use clusters to probe cosmology including dark energy. A rich dataset and many mathematical and statistical ideas already exist, that can form the basis of solving this problem. In particular, this project will focus on the modelling and statistical challenges involved in combining the strong-lensing and weak-lensing signals to constrain the internal structure of clusters. In Birmingham we have published already the independent strong- and weak-lensing analyses of the LoCuSS sample of galaxy clusters (Richard, Smith, et al. 2010; Okabe & Smith 2016). These data will form the basis of the project, that will explore the statistical and mathematical methods required to combine these constraints in an optimal and elegant manner. This project will suit a student who is proficient in computer programming and comfortable with statistical methods, whilst also enjoying engaging fully with the physics of the problem at hand. It is likely that the student will have the opportunity to join LSST as a Junior Affiliate through this project.

For more information please contact Dr. Will Farr(wfarr[at]star.sr.bham.ac.uk) or Dr. Graham Smith (gps[at]star.sr.bham.ac.uk)