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Modern South Africa astronomy and cosmology

Cosmologists seek to understand the structure and evolution of the universe and its physical constituents. A field that lies at the interface of astronomy and particle physics, cosmology has undergone a major revolution over the past decade, made possible by a wealth of observational data from cutting-edge experiments and telescopes. The wide range of these cosmological observations is impressively fit by a simple concordance model with a small number of parameters.
Modern South African Astronomy and Cosmology: Confronting the Simulated and the Observed Universe

The standard cosmological model describes an expanding universe that is smooth on the largest scales with inhomogenous structures, such as galaxies, galaxy clusters and super-clusters, present on smaller scales. These structures originated from small fluctuations, or irregularities, that were present in the matter distribution in earlier times and which then steadily grew via gravitational instability to form the variety of observed structures. In addition to the familiar, visible matter there is strong evidence that the universe contains significant fractions of dark matter and dark energy that dominate the cosmic energy budget today.

Despite the remarkable success the cosmological model has enjoyed, there are several outstanding issues that remain. The leading challenges in cosmology are:

  • to understand the nature of dark energy,
  • to understand the origin and evolution of galaxies and galaxy clusters, and
  • to describe the nature of the primordial fluctuations that seeded cosmic structure.

Major national and international astronomical facilities will help address these questions and further transform our understanding of the cosmos. All three investigators on this research will play a leading role in cosmological surveys on those facilities. The researchers at UKZN, UWC, UCT and NASSP will be involved in a large telescopic survey of supernovae and galaxy clusters on the Southern African Large Telescope. This data will be used in conjunction with photometric data from the Sloan Digital Sky survey (SDSS) and microwave data from the Atacama cosmology Telescope (ACT) to study the use of supernovae and galaxy clusters, respectively, as probes of the dark energy. Both the SDSS and the ACT projects are high-profile international projects, of which the researchers are members. The microwave data from ACT can be combined with Wilkinson Microwave Anisotropy Probe (WMAP) data and future polarization data to set strong constraints on the nature of the primordial fluctuations. The South African MeerKAT radio telescope project will map out the distribution of neutral hydrogen (cold gas) in galaxies at intermediate redshift. The cold gas plays a pivotal role in galaxy and cluster evolution.

With the wealth of incoming data, cosmology has now entered the high-precision era. To analyse and interpret this data and to use it to constrain theoretical models requires significant computational effort. Large cosmological N-body simulations are necessary to understand the distribution of large-scale structures and the complicated gas physics that influence how galaxies and galaxy clusters evolve. These simulations are also used as an impetus to understand the yield of astronomical targets (supernovae, galaxy clusters) in large cosmological surveys in different wave bands. Computationally intensive algorithms that maximise the constraints on dark energy from large supernovae surveys are necessary to design optimal surveys. The N-body and hydrodynamic simulations are also used to study the systematic effects that arise in large observational surveys, and to calibrate these effects when studying real data – issues that will be studied for microwave observations. Large Monte Carlo Markov Chain simulations are necessary to estimate cosmological parameters from the variety of data sets resulting from these observational surveys, thereby further refining the cosmological model. The CHPC provides an unprecedented opportunity to complete this computationally intensive programme that will help to address leading cosmological questions.


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