Formation and evolution of early-type galaxies: spectro-photometry from cosmo-chemo-dynamical simulations

Context. One of the major challenges in modern astrophysics is to understand the origin and the evolution of galaxies, the bright, massive early type galaxies (ETGs) in particular. There is strong observational evidence that massive ETGs are already in place at redshift z ~ 2–3 and that they formed most of their stars well before z = 1. Therefore, these galaxies are likely to be good probes of galaxy evolution, star formation and, metal enrichment in the early Universe. Aims. In this context it is very important to set up a diagnostic tool able to combine results from chemo-dynamical N-Body-TSPH (NB-TSPH) simulations of ETGs with those of spectro-photometric population synthesis and evolution so that all key properties of galaxies can be investigated. These go from the integrated spectrum and magnitudes in any photometry, both in the rest-frame and as a function of the redshift, to present-day structural properties. The main goal of this paper is to provide a preliminary validation of the software package before applying it to the analysis of observational data. Methods. The galaxy models in use where calculated by the Padova group in two different cosmological scenarios: the standard cold dark matter cosmology (SCDM), and the so-called Concordance cosmology (Λ CDM, with $\Omega_\Lambda$ = 0.762). For these template galaxies, we recover their spectro-photometric evolution through the entire history of the Universe. This is done in particular for two important photometric systems, the Bessell-Brett and the Sloan Digital Sky Survey (SDSS) passbands. Results. We computed magnitudes and colors and their evolution with the redshift along with the evolutionary and cosmological corrections for the model galaxies at our disposal, and compared them with data for ETGs taken from the COSMOS and the GOODS databases. Finally, starting from the dynamical simulations and photometric models at our disposal, we created synthetic images in a given photometric system, from which we derived the structural and morphological parameters. In addition to this, we address the question of the scaling relations, and in particular we examine the one by Kormendy. The theoretical results are compared with observational data of ETGs selected form the SDSS database. Conclusions. The simulated colors for the different cosmological scenarios follow the general trend shown by galaxies of the COSMOS and GOODS surveys at lower redshifts and are in good agreement with the data up to z ~ 1, where the number of early-type galaxies observed falls abruptly. In conclusion, within the redshift range considered, all the simulated colors reproduce the observational data quite well. Looking at the structural parameters derived from the surface imaging, the luminosities and effective radii (Kormendy relation) measured for our model galaxies are consistent with the archival data from the SDSS