Euclid VIII. Populating a dark universe using SciPIC

High-fidelity galaxy mocks are crucial for validating analysis pipelines and for cosmological inference. In this context, the Science Pipeline at PIC (SciPIC) is a pipeline specifically designed for the fast generation of synthetic galaxy catalogues from the halo properties identified in cosmological simulations. SciPIC delivers galaxy catalogues that aim to reproduce the observed luminosity function and clustering above a given flux detection limit over a wide redshift range. In this work, we introduce SciPICal, an automated pipeline that calibrates the parameters that set the main mock galaxy properties, namely number density, luminosities, colours, and positions. The pipeline was applied to the Euclid Flagship 2 Wide and Deep halo catalogues, specifically built to support the Euclid wide and deep surveys. Compared to the recently released Flagship 2 Wide mock, our calibrated version improves the clustering predictions by approximately 50% based on chi-squared values. Furthermore, we produced the Euclid Deep mock catalogue, which reaches up to z = 10 by populating a light cone and a complementary snapshot at z = 0. We validated these catalogues using measurements from spectroscopic and photometric galaxy surveys, as well as with results from a hydrodynamical simulation. The obtained good agreement (within 15% for most of the samples) in the clustering predictions across the di fferent galaxy samples considered, validates our calibration strategy and demonstrates the strong predictive power of the generated mocks. This pipeline will allow us to improve the methodology applied for assigning the galaxy properties and will ensure that the galaxy mocks remain up-to-date by incorporating constraints from upcoming observational data into the calibration procedure.