Euclid Understanding the Nature of Dark Energy and Dark Matter

Overview

Euclid is a candidate European Space Agency (ESA) M-class mission to study the geometry and nature of the dark Universe. The mission would have contributions from ESA member states and potential participation from NASA. The Euclid mission has been optimized for the measurement of two probes sensitive to dark energy:

(1) Weak Lensing (WL) — Observing the apparent distortion of the images of galaxies caused by gravitational light deflection from invisible foreground mass concentra- tions (dark matter) and modified by the expansion of the Universe. From the shape correlation between galaxies as a function of angular scales and redshift, it is possible to determine the properties of the dark energy component. Two spacecraft concepts have been studied during the assessment phase: (left) concept from EAS Astrium, and (right) concept from Thales Alenia Space. (2) Baryon Acoustic Oscillations (BAO) — Observing the imprint of sound waves from the epoch of recombina- tion. These waves imprint a standard preferential distance 1. Dark Energy Properties. Measure the dark energy equa- among galaxies that increases as the Universe ages and tion of state parameters, wp and wa, to a precision of 2 per- expands. As a standard ruler, the BAO provide Euclid with cent and 10 percent, respectively, using both expansion accurate measurements of the Hubble parameter and the history and structure growth constraints. angular diameter distance, thereby putting constraints on the properties of dark energy. 2. Beyond Einstein’s Gravity. Distinguish General Relativity from modified-gravity theories by measuring the galaxy Although Euclid has been optimized for dark energy clustering growth factor exponent, g, with a precision of surveys, the data it gathers will enable unprecedented 2 percent. advances across the range of astrophysics topics. Euclid will deliver high-quality morphologies, masses, and star- 3. The Nature of Dark Matter. Test the cold dark matter formation rates for billions of galaxies out to z~2, over the paradigm for structure formation, and measure the sum entire extragalactic sky. In addition, it will provide vital of the neutrino masses to a precision better than 0.04 eV information on objects in our own Solar System, probe the when combined with results from the Planck mission. history of the Milky Way halo, and determine the contri- bution of the light of the first stars to the IR background 4. The Seeds of Cosmic Structure. Improve by a factor of fluctuations. 20 the determination of the initial condition parameters compared to Planck alone. These parameters include the Euclid Science Objectives index of primordial power spectrum fluctuations, n, the

power spectrum amplitude, σ8, and the non-gaussianity Euclid incorporates four main science objectives: parameter, fNL. Mission Parameters The NISP imaging photometer mode contains three filters: Y, J, H in the 1–2 micron wavelength range. Launch End 2018 (Kourou) Launch Vehicle Soyuz ST2-1B The NISP slitless spectrometer mode contains two grisms and two filters, to provide spectra in two bands with two Launch Capability 2160 kg orthogonal directions. This mode has spectral resolution Orbit Sun–Earth L2 λ/∆λ~250 over two pixels. Nominal Mission 5 years Operations Euclid Surveys Euclid will provide science data downlink with K-band Euclid’s Wide Survey will cover the entire extragalactic sky telemetry and 4 hours ground station contact. Command- with galactic latitude |b|>30 deg. The Wide Survey will ing and housekeeping data will be provided with X-band achieve galaxy shear measurements for 30–40 galaxies/ telemetry. The compressed science data rate is 850 Gbits/ 2 arcmin , and spectroscopic measurements for 40 million day. galaxies with a redshift accuracy of ∆z <0.001(1+z). Mission operations will be conducted from the European Euclid’s Deep Survey will be 2 magnitudes deeper than the Science Operations Center (ESOC), Darmstadt (Germa- 2 Wide Survey, and cover a total of approximately 40 deg ny); science operations will be conducted from the Euro- 2 in patches of greater than 10 deg . pean Space Astronomy Center (ESAC), Madrid (Spain).

Payload NASA is preparing for the possibility of a significant U.S. role in Euclid. A project office has been established at the The Euclid payload will consist of a 1.2-m Korsch TMA Jet Propulsion Laboratory, with David Gallagher as the telescope feeding two instruments via a dichroic beam acting Project Manager and Michael Seiffert as the acting splitter. Project Scientist. One of NASA’s contributions would be the NISP detectors, with Goddard Space Flight Center The VIS (visible-band imager) instrument has one wave- leading that activity. The Infrared Processing and Analy- length band from 550–900 nm. The VIS focal plane sis Center (IPAC) would host the NASA Euclid Science 2 consists of 36 4k × 4k CCDs, covering a 0.5 deg field of Center. view with 100 milliarcsecond pixels. Euclid is a candidate M-class mission in the ESA Cos- The NISP (near-infrared spectrophotometer) instrument mic Vision 2015–2025 Plan. NASA involvement in this provides both imaging and spectral modes, with mode mission is subject to selection in the ESA Cosmic Vision selection via a filter wheel. The NISP focal plane consists program and to NASA budgetary constraints. of 16 2k × 2k infrared detectors, covering a 0.5 deg2 field of view with 300 milliarcsecond pixels.

National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California www.nasa.gov

JPL 400-1422 01/11

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