Euclid Definition Study Report (1110.3193v1)

Abstract: Euclid is a space-based survey mission from the European Space Agency designed to understand the origin of the Universe's accelerating expansion. It will use cosmological probes to investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of structure formation. The mission is optimised for two independent primary cosmological probes: Weak gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). The Euclid payload consists of a 1.2 m Korsch telescope designed to provide a large field of view. It carries two instruments with a common field-of-view of ~0.54 deg2: the visual imager (VIS) and the near infrared instrument (NISP) which contains a slitless spectrometer and a three bands photometer. The Euclid wide survey will cover 15,000 deg2 of the extragalactic sky and is complemented by two 20 deg2 deep fields. For WL, Euclid measures the shapes of 30-40 resolved galaxies per arcmin2 in one broad visible R+I+Z band (550-920 nm). The photometric redshifts for these galaxies reach a precision of dz/(1+z) < 0.05. They are derived from three additional Euclid NIR bands (Y, J, H in the range 0.92-2.0 micron), complemented by ground based photometry in visible bands derived from public data or through engaged collaborations. The BAO are determined from a spectroscopic survey with a redshift accuracy dz/(1+z) =0.001. The slitless spectrometer, with spectral resolution ~250, predominantly detects Ha emission line galaxies. Euclid is a Medium Class mission of the ESA Cosmic Vision 2015-2025 programme, with a foreseen launch date in 2019. This report (also known as the Euclid Red Book) describes the outcome of the Phase A study.

Overview of the Euclid Mission: Mapping the Geometry of the Dark Universe

The European Space Agency's Euclid mission is a pivotal undertaking in cosmology, aimed at unraveling the intricate nature of dark energy and dark matter by mapping the Universe's geometry. This essay provides an expert overview of the Euclid Definition Study Report, detailing the mission's objectives, methodology, and potential scientific impact.

Scientific Objectives

Euclid is designed to enhance our understanding of the Universe's expansion by investigating dark energy and dark matter. The mission's primary scientific objectives are to reach a dark energy Figure of Merit (FoM) greater than 400 through weak lensing and galaxy clustering, precisely measure the growth exponent γ with a precision of less than 0.02, test the Cold Dark Matter paradigm, and constrain the spectral index of the primordial power spectrum with percent-level accuracy in conjunction with Planck data.

Methodology and Instrumentation

Euclid will achieve its goals through two principal cosmological probes: Weak Lensing (WL) and Baryonic Acoustic Oscillations (BAO). WL will map dark matter and assess dark energy by examining galaxy shape distortions, while BAO will provide a cosmic ruler to measure the Universe's expansion. These measurements require an accurate assessment of cosmic structure, demanding high-precision photometric and redshift data.

The payload consists of a 1.2 m telescope and two instruments: the visible imaging instrument (VIS) and the Near-Infrared Spectrometer and Photometer (NISP). VIS is tasked with providing high-quality images necessary for measuring weak lensing shear, while NISP performs near-infrared imaging for photometric redshifts and spectroscopy for precise redshift measurements.

Surveys and Data Handling

Euclid will conduct a wide survey covering 15,000 square degrees of extragalactic sky, capturing photometric and redshift data needed for its cosmological analyses. A deep field survey will be conducted at higher sensitivities to calibrate the slitless spectroscopy and monitor stability. Data handling is managed through the Science Ground Segment (SGS), which involves processing and archiving the vast quantities of data generated by the mission.

Performance and Simulations

Extensive simulations ensure the instrument and mission design meet scientific requirements, with specific focus on the accuracy of the shape measurements and photometric redshifts necessary for weak lensing studies, along with the redshift precision for galaxy clustering. Simulation results demonstrate that Euclid can achieve the necessary sensitivity and systematic control to address its scientific goals.

Conclusion and Implications

Euclid is poised to provide unprecedented insights into the fundamental properties of our Universe. By jointly probing cosmic structure and expansion history, the mission will test competing theories of dark energy and gravity and advance our understanding of the Universe's evolution. The project is a crucial step in exploring cosmological parameters with an accuracy required for testing the standard model of cosmology and branching into new physics.

Euclid's results will likely inform the next generation of cosmological models and potentially reveal new facets of the Universe that challenge our current understanding, opening doors for further theoretical and observational advancements in cosmology.