Colour-magnitude diagram in simulations of galaxy formation

State-of-the-art cosmological hydrodynamical simulations have star particles with a typical mass between ∼108 and ∼103 M⊙ according to resolution, and treat them as simple stellar populations. On the other hand, observations in nearby galaxies resolve individual stars and provide us with single star properties. An accurate and fair comparison between predictions from simulations and observations is a crucial task. We introduce a novel approach to consistently populate star particles with stars. We developed a technique to generate a theoretical catalogue of mock stars whose characteristics are derived from the properties of parent star particles from a cosmological simulation. Also, a library of stellar evolutionary tracks and synthetic spectra is used to mimic the photometric properties of mock stars. The aim of this tool is to produce a data base of synthetic stars from the properties of