A comprehensive galaxy and AGN mock catalogue for the next generation of surveys

Current and future large-sky surveys will produce unprecedented amounts of photometric and spectroscopic data for billions of sources. To fully exploit the scientific potential of these surveys, realistic simulations of astrophysical sources such as galaxies and Active Galactic Nuclei (AGN) have become essential tools. In this context, we introduce a new, flexible, and efficient computational model designed to simulate mock catalogues of galaxies and AGN that accurately replicate the statistical properties and observational features of these astrophysical sources. To achieve this, we followed a completely empirical approach, that is, we calibrated the model based on observed scaling relations. Specifically, we started with simulated dark matter (DM) haloes from an N-body simulation, to preserve the link with the cosmic web, and we populated them with galaxies and AGN using abundance matching techniques. To achieve this, we used several observational inputs, such as stellar mass functions, host galaxy AGN mass functions, and AGN accretion rate distribution functions studied at different redshifts to assign, among other properties, stellar masses, the fraction of quenched galaxies, or the AGN activity (demography, obscuration, multiwavelength emission, etc.). As a proof test, we applied the method to a Millennium DM lightcone of 3.14 deg2 up to a redshift of z = 10. We show that the AGN population from the mock lightcone presented here reproduces with good accuracy various observables, such as state-of-the-art luminosity functions in the X-ray and in the ultraviolet, near-infrared colour-colour diagrams, and narrow emission line diagnostic diagrams. Finally, we demonstrate several applications of this catalogue. We computed several forecasts of Euclid observations, and we tested a pipeline for retrieving photometric redshifts on simulated AGN with Euclid-like photometry and a spectroscopic analysis pipeline on Euclid-like AGN spectral energy distributions. Finally, we show an application of this model for the preparation of an X-ray observational campaign.