  The next generation of wide spectroscopic surveys such as Euclid will scan
the sky in the near-infrared to obtain both photometry and spectroscopy. For
this purpose, the Euclid telescope will rely on a Near-Infrared Spectrometer
and Photometer (NISP) instrument whose spectroscopic channel has been designed
to operate in slitless configuration. This powerful and easy to operate
configuration makes it possible to avoid any prior selection on the targeted
galaxies while covering the entire field of view. Beyond the observed flux of
the galaxy, the detector capabilities will strongly depend on the shape of the
galaxy, which gets convolved with the galaxy spectra. To test the effect of the
galaxy shape on the quality of the Euclid slitless spectra, we have performed
simulations testing potentially impactful morphological parameters. We then
characterized the effect of the disk half-light radius on the quality of the
Euclid slitless spectra.
