Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

This paper presents the specification, design, and development of the Visible Camera (VIS) on the European Space Agency’s Euclid mission. VIS is a large optical-band imager with a field of view of 0.54 deg2 sampled at 000 . 1 with an array of 609 Megapixels and a spatial resolution of 000 . 18. It will be used to survey approximately 14 000 deg2 of extragalactic sky to measure the distortion of galaxies in the redshift range z = 0.1–1.5 resulting from weak gravitational lensing, one of the two principal cosmology probes leveraged by Euclid. With photometric redshifts, the distribution of dark matter can be mapped in three dimensions, and the extent to which this has changed with look-back time can be used to constrain the nature of dark energy and theories of gravity. The entire VIS focal plane will be transmitted to provide the largest images of the Universe from space to date, specified to reach mAB ≥ 24.5 with a signal-to-noise ratio S/N ≥ 10 in a single broad IE ≃ (r + i + z) band over a six-year survey. The particularly challenging aspects of the instrument are the control and calibration of observational biases, which lead to stringent performance requirements and calibration regimes. With its combination of spatial resolution, calibration knowledge, depth, and area covering most of the extra-Galactic sky, VIS will also provide a legacy data set for many other fields. This paper discusses the rationale behind the conception of VIS and describes the instrument design and development, before reporting the prelaunch performance derived from ground calibrations and brief results from the in-orbit commissioning. VIS should reach fainter than mAB = 25 with S/N ≥ 10 for galaxies with a full width at half maximum of 000 . 3 in a 100 . 3 diameter aperture over the Wide Survey, and mAB ≥ 26.4 for a Deep Survey that will cover more than 50 deg2. The paper also describes how the instrument works with the Euclid telescope and survey, and with the science data processing, to extract the cosmological information.

Abstract:

The Near-Infrared Spectrometer and Photometer (NISP) on board the Euclid satellite provides multiband photometry and R â ³ 450 slitless grism spectroscopy in the 950- 2020 nm wavelength range. In this reference article, we illuminate the background of NISP' s functional and calibration requirements, describe the instrument' s integral components, and provide all its key properties. We also sketch the processes needed to understand how NISP operates and is calibrated as well as its technical potentials and limitations. Links to articles providing more details and the technical background are included. The NISP' s 16 HAWAII-2RG (H2RG) detectors with a plate scale of 03.3 pixel-1 deliver a field of view of 0.57 deg2. In photometric mode, NISP reaches a limiting magnitude of ~24.5 AB mag in three photometric exposures of about 100 s in exposure time for point sources and with a S/N of five. For spectroscopy, NISP' s pointsource sensitivity is a signal-to-noise ratio = 3.5 detection of an emission line with flux 2 10-16 erg s-1 cm-2 integrated over two resolution elements of 13.4 in 3-560 s grism exposures at 1.6 μm (redshifted Hα). Our calibration includes on-ground and in-flight characterisation and monitoring of the pixel-based detector baseline, dark current, non-linearity, and sensitivity to guarantee a relative photometric accuracy better than 1.5% and a relative spectrophotometry better than 0.7%. The wavelength calibration must be accurate to 5 or better. The NISP is the state-of-the-art instrument in the near-infrared for all science beyond small areas available from HST and JWST - and it represents an enormous advance from any existing instrumentation due to its combination of field size and high throughput of telescope and instrument. During Euclid' s six-year survey covering 14 000 deg2 of extragalactic sky, NISP will be the backbone in determining distances of more than a billion galaxies. Its near-infrared data will become a rich reference imaging and spectroscopy data set for the coming decades.