School of Physics and Astronomy

Mapping the cosmic horizon with next-generation surveys

Research Group:Cosmology and Relativity (Astronomy Unit)

Number of Students:1

Full-time Project: yes


STFC or College studentships

Project Description:

On the distance scales probed by current galaxy surveys, General Relativistic effects are only mildly important, and most of the interpretation of the data can be done within the context of Newtonian gravity. Forthcoming surveys like LSST, SKA, and Euclid are much bigger and deeper than their predecessors though, and so will be able to probe much larger scales - approaching the size of the cosmic horizon - where GR effects are important and must be taken into account.

Excitingly, the observable signatures of these effects should contain valuable information about some of the most fundamental questions in cosmology and theoretical physics - the nature of gravity, the cause of cosmic acceleration, and how inflation set the initial conditions of the Universe we see today. By measuring them, we can test fundamental physics on truly cosmological scales.

The aim of this project is to put together a suite of tools for making practical measurements of GR effects on the very largest observable distance scales in the Universe. Because of an effect called cosmic variance, these measurements can only be made if data from several different large-scale surveys can be combined in a precise, statistically-robust way, with excellent rejection of systematic effects that contaminate the data. Only a few preliminary studies have attempted to use this 'multi-tracer' method so far, and substantial advances in modelling and statistical analysis methods are urgently needed to make it usable in future surveys.

This project will develop the most important components of this method, with a view to using it on simulations, precursor datasets, and eventually the large surveys themselves. The work will include:

  • Performing theoretical calculations to understand how the large-scale signal changes in different cosmological scenarios
  • Building realistic simulations of the signal, incorporating models of how galaxies trace the matter distribution
  • Simulations of systematic errors in the data caused by astrophysical contamination and the instrumental responses of optical and radio telescopes
  • Development of new statistical analysis methods that can clean out systematic effects and recover the true signal with sufficient precision

Through this project, you will gain skills and experience in a range of important topics across cosmology and astrophysics: performing calculations using cosmological perturbation theory; running and analysing N-body simulations; applying galaxy-halo models to simulations and data; simulating data produced by optical and radio telescopes; working with Bayesian statistical analysis methods; and writing efficient parallel computer codes. You will also gain experience working in large scientific collaborations, where you will develop project management and communication skills, and have the opportunity to attend international meetings and work with international collaborators in the US, South Africa, and Italy.

SPA Academics: Phil Bull