Centre for Extragalactic Astronomy

Imaging Surveys: Cosmology via Quasars and Galaxy Clusters

Evidence from the high redshift supernova Hubble diagram suggests that the expansion of the Universe is accelerating. If this acceleration is driven by Dark Energy then the immediate interest is to derive the dark energy equation of state and its evolution with redshift. The next generation of wide-field surveys provide powerful tools to address such fundamental questions via baryon acoustic oscillations and redshift space distortions, as well as other controversial cosmological questions such as the amplitude of dark matter fluctuations on ~8Mpc scales.

We are currently preparing to exploit new cosmological surveys with potentially as much impact as the previous Sloan Digital Sky Survey and 2dF Galaxy Redshift surveys. We first wish to exploit a new generation of imaging surveys, principally the ESO VLT Survey Telescope (VST) ATLAS (PI Shanks) and the VISTA VIKING (PI Edge) surveys and their various extensions. These surveys, when combined with their twin VISTA Hemisphere and VST KiDS surveys, provide optical-near-IR ugrizYJHK coverage over much of the Southern Hemisphere. ATLAS has already covered ~4000 sq deg of sky.

The VST imaging telescope shortly after commissioning in August 2011.
A major aim is to combine these multi-wavelength imaging surveys with the power of the forthcoming eROSITA X-ray survey to make catalogues of X-ray quasars and galaxy clusters identified in the optical and NIR. Spectroscopic redshifts can then be measured using new multi-object spectrographs like ESO VISTA 4MOST to make redshift surveys of a million quasars out to z~2.5 and ~50000 rich clusters out to z>1. The quasar survey can then be used to make highly competitive measurements of dark energy parameters via quasar clustering. The cluster survey will characterise their space density evolution out to z~1 to probe the apparent deficiency of clusters detected by Planck SZ measurements and a new measurement of the crucial dark matter fluctuation parameter, sigma_8. As well as for these cosmological purposes, the surveys will also be used to throw new light on quasar and cluster physics, including quasar black hole demographics and cluster gaseous content.

Staff involved with this project at Durham include Tom Shanks, Alastair Edge, Peder Norberg and Nigel Metcalfe.