A key tool to probe Euclid spectroscopy: Spectro-Photometric simulations of galaxies to unravel NISP's capabilities.

We present in this master Thesis the construction of Spectral Energy Distribution (SED) of galaxies located at 0.3 $\leq z \leq$ 2.5. The constructed SEDs will go through the Euclid Near Infrared Spectrometer and Photometer (NISP) simulator hosted in the Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF; INAF) at Milan, aiming at reproducing spectra expected from the NISP mounted on the Euclid telescope. These simulations will enable evaluating the spectroscopic survey performances of the Euclid mission, and confirming that the telescope and its slitless NISP spectrometer will satisfy the required detection limits for nebular emission lines. This project was conceived in synergy with the Euclid Legacy Science Working Groups (SWGs), as a "PILOT RUN" simulation test for spectroscopic data. The PILOT RUN includes a study of the capabilities expected from the Euclid Wide and Deep fields' configurations. The construction of the incident SEDs consists in computing a continuum using the Bruzual \& Charlot(2003) models, calling out best-fit SED parameters available in the catalogs. The nebular emission Balmer, [NII]$\lambda\lambda$6584,6549, [OII]$\lambda\lambda$3727,3729, [OIII]$\lambda\lambda$5007,4959, [SII]$\lambda\lambda$6731,6717, [SIII]$\lambda\lambda$9531,9069 and Paschen lines are added making use of calibrations available in literature. We refer to common tools and indicators for emission lines analysis such as the Star Formation Rate (SFR), the Baldwin-Phillips-Terlevich diagram (BTP), the Mass-Metallicity Relation (MZR) and photoionization models. The emission lines are then integrated to the continuum accounting for the calculated velocity dispersion of each galaxy. A photometric and spectroscopic comparison of the incident SEDs with observational data is presented in this Thesis. The incident SEDs then go through the Euclid NISP simulator that mimic the spectra expected from the NISP spectrometer, generating the simulated spectra. The PILOT RUN simulations are still ongoing, only part of the simulated spectra have been constructed, limited to the galaxies from the CANDELS/GOODS-N catalog, corresponding to one out of the 5 pointings planned to reach the required Deep Survey configuration, in terms of exposure time. This pointing exactly matches the exposure time required for the Wide Survey configuration. Thus, we present in this Thesis a first analysis of the available simulated data, and provide a confirmation of the detection limit specifications for the continuum (i.e. H(AB) $\geq$ 19.5 mag) and emission lines (i.e. Flux $\geq2\times10^{-16}$ erg cm\textsuperscript{-2} s\textsuperscript{-1} \mathrm{\AA}\textsuperscript{-1}) of the Euclid Wide Survey. The full set of the PILOT RUN simulations will extensively complete the first picture given by our preliminary analysis. We also provide an estimate of the NISP spectral resolution and finally present an analysis stacking spectra located at 1.6 $\leq z \leq$ 2.0, attesting for the great potential of the method in confirming redshift determination, a crucial aspect for the Euclid mission.