Peter Thomas


Galaxy formation using world-leading numerical simulations and observational surveys

Supervisor: Peter Thomas


  • Jon Loveday, Seb Oliver, Kath Romer, Mark Sargent, Stephen Wilkins (Sussex)
  • Bruno Henriques (Munich) - semi-analytic modelling
  • Virgo Supercomputing Consortium (Durham, Munich) - large-scale numerical simulations.

Funding: STFC quota studentship.

Understanding galaxy formation is one of the key challenges in extragalactic astronomy. Naive models fail miserably to explain the luminost function of galaxies, predicting both too many dwarfs and too many massive galaxies. To cure this problem by putting in feedback requires both (i) extremely large energy input into the interstellar medium from supernovae, ejecting the majority of the cold gas in dwarf galaxies into the inter-galactic medium, and (ii) efficient coupling of emission from active galactic nuclei (AGN, supermassive black holes) into both the host galaxy and the surroundings.

Sussex has experience in many aspects of this problem:

  • Peter Thomas is a founding member of the Virgo Supercomputing Consortium that is undertaking some of the largest simulations of the formation of structure in the Universe. These have been used to produce "merger trees" that follow the formation and growth of the dark matter halos within which galaxies form. We then use these to make "semi-analytic" models (SAMs) of the galaxies themselves. The result is an extra-ordinary success in matching the properties of the galaxy population that we see around us today. However, there are a number of lurking problems, not least of which is the excessive feedback required from both supernovae and AGN, and the excessive production of metals at high-redshift.
  • THe Virgo Consortium is also undertaking massive hydrodynamical simulations of galaxy formation. These are necessarily restricted in size but have the major advantage that they follow the cycling of material between galaxies and the intergalactic medium. We can use the simulations to test and refine many of the assumptions that get built into our SAMs.
  • Other members of the Astronomy Centre have access to the latest observational data-sets that probe galaxy formation in unprecedented detail in both the nearby Universe and out to high red-shifts. These include GAMA - a multiwavelength study in the nearby Universe; VISTA VHS (wide) and VIDEO (deep) near-infrared surveys; HerMES - far-infra-red galaxy survey; DES - optical/near-IR survey of over 300 million galaxies; HST - deep observations of very distant galaxies at high redshift; ALMA - probing molecular gas in galaxies; LOFAR - detecting the signatures of reionization by light from the first galaxies.

The juxtaposition of this modelling and observational expertise at Sussex makes it an ideal place to attack this problem. Within the next few years we would expect to make major advances in our understanding of galaxy formation.

Project outline

  • Year 1: Background reading; learning to use existing semi-analytic galaxy formation models; exposure to observational data sets.
  • Year 2: Testing existing models against new observational data. Write papers on same. Present work at national conference.
  • Year 3: Extend models to include new physics that better matches the observations. Write papers and thesis. Present work at international conference.

The specfic aspects of galaxies that will be studied will be determined at the start of the project but may include: observational properties of the first, very high-redshift gaalxies; the evolution of metallicity; the properties of the intergalactic medium; the interaction of galaxies with their environment; the star-formatiion history of dwarf galaxies.

The student will be expected to visit collaborators within the UK and Europe at all stages of their PhD.