redshift 6-8 universe. Both surveys will be carried out in visible and near-infrared bands and also include spectroscopic measurements in the near-infrared. Figure 2.1 indicates the sensitivities for the Euclid wide survey; the deep survey will go approximately 6 times (2 magnitudes) fainter. The Euclid Wide Survey is expected to cover a larger area than will the WFIRST survey.

The Euclid surveys will be unprecedented, producing a massive data set of deep images and spectra covering a significant fraction of the sky. The Euclid Wide Survey will provide images of billions of galaxies at redshifts of 1 < z < 3 and near-infrared spectroscopy of tens of millions of galaxies, thereby allowing determination of their redshifts. Its 0.13 arcsecond spatial resolution in the visible will be a significant improvement over ground-based surveys whose resolution is limited because of the atmosphere. The Euclid Deep Survey is designed primarily to detect and study a sample of high-redshift star-forming galaxies at 6 < z < 8, thus providing new insights into galaxy formation and evolution at early epochs.10 The Euclid surveys will be a unique resource for the astronomical community, not unlike the earlier Sloan Digital Sky Survey, and can be expected to impact all areas of astronomical research. In addition to the obvious impact on studies of galaxies at moderate and high redshifts, the Euclid surveys will also provide a vast catalogue of stars in our own Galaxy and in nearby galaxies, expected to make important contributions to studies of both galaxy structure and stellar populations.

U.S. participation in Euclid through the Euclid Science Team (EST) and Euclid Consortium (EC) could be very beneficial for the development of the tools and expertise within the U.S. astronomical community needed to effectively exploit the Euclid survey data when it becomes public, nominally 14 months after the start of the survey. Access to and widespread use of the Euclid survey data will help leverage the considerable investment made by the United States in both JWST and large ground-based projects such as Large Synoptic Survey Telescope (LSST) and the Atacama Large Millimeter Array.

THE PROPOSED WFIRST MISSION

Finding: The Wide Field Infrared Survey Telescope (WFIRST) is a highly capable mission with an exciting and broad scientific program spanning exoplanets to cosmology to infrared surveys.

NWNH envisaged WFIRST to be a 1.5-meter obscured-aperture telescope; recent work by the Science Definition Team (SDT) has suggested an alternate 1.3-meter off-axis telescope design, with equivalent detecting area but a more compact point spread function.11 In this new candidate design, the focal plane consists of 36 2k x 2k HgCdTe infrared detectors, of which 8 are dedicated to distinct spectroscopic channels with 0.45 arcseconds per pixel and spectral resolution R ∼ 200.12 The imaging scale is approximately 0.18 arcseconds per pixel with a 0.291 degree field of view. Spectroscopy is always enabled in parallel with the imaging arrays and covers 1.1 to 2.0 microns. A filter wheel for the imaging array also includes six filters and an additional R ∼ 75 prism. WFIRST can take images and spectra over the 0.6 to 2.0 micron wavelength range.

WFIRST enables a broad spectrum of science and the large discovery potential of a guest observer program. The Euclid and WFIRST missions have different objectives, different hardware, and different survey designs. Euclid will make high-resolution optical images that are the key observation for its core program of using weak lensing to study dark energy. WFIRST use its near-infrared observations to address the broad research program outlined in NWNH.

COMPARISON OF WFIRST AND EUCLID CAPABILITIES

Finding: Both Euclid and WFIRST should make important contributions to the understanding of cosmic acceleration. While Euclid should advance our understanding of



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