Euclid is a proposed space telescope being developed with the European Space Agency (ESA) for launch around 2018. It is planned to observe the whole sky with the same image quality as the Hubble Space Telescope and measure the rainbow of colours (spectra) within millions of galaxies. These very high quality imaging observations will be used to investigate dark energy using cosmic lensing. The precise three dimensional positions of galaxies obtained from the spectra will be used to study the clustering of galaxies. The imaging science part of the mission is described in detail in the Euclid Imaging Consortium Science Book.
At the UCL Department of Physics and Astronomy, we are heavily involved in preparations for the imaging survey. We lead studies to determine the requirements cosmic lensing places on the optical design of the instrument. We are also studying the impact of choice of optical filters on the accuracy of the photometric redshift measurements and working on the requirements for spectroscopic training sets. Among other work, we have made forecasts for the cosmological constraints on dark energy in the presence of intrinsic alignments between galaxies that arise during galaxy formation.
Much of the current activity focuses on the core science which drives the mission design. However, it is clear that high resolution imaging of the entire extragalactic sky has tremendous value beyond the study of dark energy using cosmic lensing and galaxy clustering. This includes high resolution imaging of over two billion galaxies in the visible and infra-red parts of the spectrum which could, for example, be used to classify galaxies into ellipticals and spirals.