Euclid preparation: XXVII. The NISP spectroscopy channel: Ground performance and calibration

ESA's Euclid cosmology mission relies on the very sensitive and accurately calibrated spectroscopy channel of the Near-Infrared Spectrometer and Photometer (NISP). With three operational grisms in two wavelength intervals, NISP provides diffraction-limited slitless spectroscopy over a field of 0.57 deg2. A blue grism, BGE, covers the wavelength range 926- 1366 nm at a spectral resolution (ℛ) of 440- 900 for a 0.″5 diameter source with a dispersion of 1.24 nm px-1. Two red grisms, RGE, span 1206 to 1892 nm at ℛ = 550- 740 and a dispersion of 1.37 nm px-1. We describe the construction of the grisms as well as the ground testing of the flight model of the NISP instrument, where these properties were established.