Euclid Assessment Study Report for the ESA Cosmic Visions

Euclid is a proposed high-precision survey mission to map the geometry of the Dark Universe with demonstrated feasibility. Euclid's Visible - Near-InfraRed imaging and spectroscopy of the extragalactic sky will further produce extensive legacy science to the boundaries of the visible universe. The mission is optimised for two primary cosmological probes: Weak gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). Euclid's wide survey will cover 20,000 deg2, measuring shapes and redshifts of galaxies to redshift 2. For weak lensing, Euclid will measure the shape of over 2 billion galaxies with a density of 30-40 resolved galaxies per arcmin2 in one broad visible R+I+Z band (550-920 nm) down to AB mag 24.5 (10sigma). The photometric redshifts for these galaxies are derived from three additional Euclid NIR bands (Y,J,H in the range 0.92-2.0 micron) reaching AB mag 24 (5sigma) in each, complemented by photometry from ground based surveys. The BAO are determined from a NIR spectroscopic survey with a redshift accuracy of dz/(1+z) =0.001. The baseline payload consists of a Korsch telescope with a primary mirror of 1.2 m diameter and is designed to provide a large field of view (0.5 deg2) to three scientific instruments: (1) VIS: a CCD based optical imaging channel, (2) NIP: a NIR imaging photometry channel, and (3) NIS: a NIR spectrometric channel. This report presents an overview of the assessment study phase of the Euclid candidate M-class Cosmic Vision mission; it will provide a description of the Euclid science objectives, the mission implementation and payload, and the envisaged data handling.