Launched successfully on July 1st, 2023, Euclid, the M2 mission of the ESA cosmic vision program, aims mainly at understanding the origin of the accelerated expansion of the Universe. Along with a visible imager VIS, it is equipped with the NISP instrument, a Near Infrared Spectrometer and Photometer, bespoke tailored to perform a 3D mapping of the observable Universe. It operates in the near-infrared spectral range, from 900 nm to 2000 nm with 2 observing modes: as a spectrometer, the NISP instrument will permit measuring millions of galaxy spectroscopic redshifts over the 6.5 years lifetime of the Euclid mission; as a photometer, it will obtain photometric redshifts of billions of galaxies. This paper provides a description of the NISP instrument, its scientific objectives, and offers an assessment of its current performance in flight.
Euclid, the M2 mission of the ESA’s Cosmic Vision 2015-2025 program, aims to explore the Dark Universe by conducting a survey of approximately 14 000 deg2 and creating a 3D map of the observable Universe of around 1.5 billion galaxies up to redshift z ∼ 2. This mission uses two main cosmological probes: weak gravitational lensing and galaxy clustering, leveraging the high-resolution imaging capabilities of the Visual Imaging (VIS) instrument and the photometric and spectroscopic measurements of the Near Infrared Spectrometer and Photometer (NISP) instrument. This paper details some of the activities performed during the commissioning phase of the NISP instrument, following the launch of Euclid on July 1, 2023. In particular, we focus on the calibration of the NISP detectors’ baseline and on the performance of a parameter provided by the onboard data processing (called NISP Quality Factor, QF) in detecting the variability of the flux of cosmic rays hitting the NISP detectors. The NISP focal plane hosts sixteen Teledyne HAWAII-2RG (H2RG) detectors. The calibration of these detectors includes the baseline optimization, which optimizes the dynamic range and stability of the signal acquisition. Additionally, this paper investigates the impact of Solar proton flux on the NISP QF, particularly during periods of high Solar activity. Applying a selection criterion on the QF (called NISP QF Proxy), the excess counts are used to monitor the amount of charged particles hitting the NISP detectors. A good correlation was found between the Solar proton flux component above 30 MeV and the NISP QF Proxy, revealing that NISP detectors are not subject to the lower energy components, which are absorbed by the shielding provided by the spacecraft.
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