Cosmology with Galaxy Surveys

Surveys of millions of galaxies – using optical, infrared and radio telescopes – allow us to map the distribution of galaxies in parts of the Universe surrounding us. Galaxies trace the large-scale structure and their distribution contains vital clues to properties of the Universe and its ingredients, in particular Dark Matter and Dark Energy (see Large-scale Structure). The further away the galaxies are from us, the further back in time we are looking – since light travels at a finite speed. This means that galaxy surveys also allow us to trace the history of the Universe. The state of the art in galaxy surveys is represented by the Dark Energy Survey (DES, ongoing) and the Baryon Acoustic Oscillation Survey (BOSS, recently completed). New surveys are being prepared and planned – and they will detect and measure even more galaxies than DES and BOSS. In the optical and infrared part of the spectrum, two of the major new surveys for the next decade are the space-borne Euclid telescope and the ground-based Large Synoptic Survey Telescope (LSST). South Africa has a small but important participation in LSST. In the radio part of the spectrum, South Africa has recently built the 64-dish MeerKAT telescope in the Karoo, which could become the world’s best radio array until it is absorbed in the Square Kilometre Array (SKA) next decade, to form a giant 197-dish array.