EUCLID Phase A Revised

This proposal is for funding to support phase A studies for Euclid, a selected candidate M-class mission in ESA's Cosmic Vision programme. Euclid is designed to make the most exquisitely accurate measurements of Dark Energy in several complementary ways, to explore what it is, and to quantify precisely its role in the evolution of the Universe. In the current 'concordance model' of the Universe, three quarters of it consists of Dark Energy, and one fifth of Dark Matter: Euclid will measure and elucidate the nature of Dark Matter too. If, instead, the concordance model is incorrect, and our fundamental ideas about gravity need revision, Euclid will test the validity of many of these modified gravity theories. Besides Dark Energy and Dark Matter studies, Euclid will provide a truly colossal legacy dataset over the whole sky, with optical imaging at 0.25 arc second spatial resolution to very faint limits (R~24.5), infrared imaging in 3 bands to similar limits and only slightly worse spatial resolution, and spectra and redshifts of 150 million galaxies to H=22. This dataset can only be obtained from space. It will be used by scientists worldwide in a wide range of contexts, and it will have huge public outreach potential. The planned launch of Euclid is 2017. The payload instruments will be produced through national funding, so this funding supports the first part of that provision. The UK Euclid team will work with ESA to develop the overall Euclid payload concept, providing vital scientific inputs to ensure that the optimal approach is taken and to guide design tradeoffs. It will, through ESA, provide inputs to the ESA-commissioned industry studies of the mission as a whole. The team will also work with other European colleagues to develop a large-field imager with two focal planes (one optical and one infrared) and an infrared spectrograph, and has strong roles in each of these areas. The proposal contains requests for supporting the scientific studies, system engineering work at the level of Euclid, and work on the instrumentation: the visible imager (particularly the detectors and entire electronics detection chain), and the optomechanical concept and design for both the near infrared spectrograph and imager. UK groups have been working extensively through the Cosmic Vision process to contribute to Euclid through its precursor, DUNE and SPACE. They have taken central roles in the core instrumentation and in the science support to the mission and have been highly effective in shaping the mission concept. This grant will cement the leading positions for UK groups, realised up to now through their vision and commitment.