Abstract
This work focuses on the pilot run of a simulation campaign aimed at
investigating the spectroscopic capabilities of the Euclid Near-Infrared
Spectrometer and Photometer (NISP), in terms of continuum and emission line
detection in the context of galaxy evolutionary studies. To this purpose we
constructed, emulated, and analysed the spectra of 4992 star-forming galaxies
at $0.3 \leq z \leq 2.5$ using the NISP pixel-level simulator. We built the
spectral library starting from public multi-wavelength galaxy catalogues, with
value-added information on spectral energy distribution (SED) fitting results,
and from Bruzual and Charlot (2003) stellar population templates. Rest-frame
optical and near-IR nebular emission lines were included using empirical and
theoretical relations. We inferred the 3.5$\sigma$ NISP red grism spectroscopic
detection limit of the continuum measured in the $H$ band for star-forming
galaxies with a median disk half-light radius of \ang{;;0.4} at magnitude $H=
19.5\pm0.2\,$AB$\,$mag for the Euclid Wide Survey and at $H =
20.8\pm0.6\,$AB$\,$mag for the Euclid Deep Survey. We found a very good
agreement with the red grism emission line detection limit requirement for the
Wide and Deep surveys. We characterised the effect of the galaxy shape on the
detection capability of the red grism and highlighted the degradation of the
quality of the extracted spectra as the disk size increases. In particular, we
found that the extracted emission line signal to noise ratio (SNR) drops by
$\sim\,$45$\%$ when the disk size ranges from \ang{;;0.25} to \ang{;;1}. These
trends lead to a correlation between the emission line SNR and the stellar mass
of the galaxy and we demonstrate the effect in a stacking analysis unveiling
emission lines otherwise too faint to detect.