Line of research overview

Numerical models of the formation of structure in the Universe

Principal Investigator: Pierluigi Monaco

Abstract: We use various numerical techniques to simulate the formation of structures in the Universe with supercomputers. We address the formation of large-scale structure from horizon scales down to galactic scales; the astrophysics of galaxy formation is addressed treating, in N-body hydrodynamical codes, several relevant processes with effective models, or is addressed with semi-analytic models applied to simulated dark matter halo merger trees. All these techniques are used to address the following questions: how do we produce large sets of simulations, for error estimation in cosmology? what are the main physical processes responsible for the formation of galaxies and galaxy clusters? what are our forecasts for planned and future galaxy surveys?

Status of project and perspectives: The group is involved in several parallel projects of numerical cosmology. We list below progress achieved in these years, several of these projects are developed in synergy with the “Galaxy Clustering” and the “Cosmology with Galaxy Clusters” line of research, where we provide simulations and reserve the interpretative work for the other lines.

• Cosmological simulations and mock catalogs for characterizing the error budget in future galaxy surveys. We are developing and massively using the PINOCCHIO code for fast simulations; development is progressing along two main avenues, implementation of cosmologies beyond LambdaCDM (see below) and technical development for better scaling on supercomputers. The code is being used to produce 3500 huge catalogs of dark matter halos in the past lightcone, covering half of the sky and starting at redshift z=4. These simulations will be the basis for the computation of the numerical covariance matrix for the clustering of the spectroscopic galaxy sample observed by Euclid. We plan to use these simulations to provide a large set of mock galaxy catalogs to the Euclid collaboration.
• Simulations beyond Newtonian LambdaCDM. We have merged the Particle-Mesh (PM) relativistic Gevolution and the Newtonian Tree-PM Gadget-4 code, so as to have a proper relativistic treatment of clustering on large scales where the Newtonian limit neglects effects that have small but relevant observational consequences. We have developed PINOCCHIO to work with some modified gravity theories, in particular f(R) and cubic galileon. We plan to set up, in the future, an ecosystem of codes for the production of mock galaxy catalogs in a larger set of gravity theories.
• Hydro simulations for the formation of galaxies. We have progressed in our description of the sub-grid physics of galaxy formation, including innovative recipes for AGN feedback and dust evolution. We are currently working on an explicit treatment of molecular gas evolution. This allows us to progress in the sophistication of the treatment of the small-scale physics that shapes the properties of galaxies, thus improving our predictive power. These same recipes are used in simulations of galaxy clusters to understand their physics; the production of galaxy cluster simulations for cosmology is described in the “Cosmology with Galaxy Clusters” line of research.
• Semi-analytic models of galaxy formation. The GAEA semi-analytic model has been further developed, with innovative treatment of AGN feedback, metallicity evolution and a variable IMF. The model has been compared with several recent data sets, including the very deep spectroscopic VANDELS survey. A more phenomenological approach has been adopted to address reionization, with special attention to the relative role of galaxies and AGNs in provinding the required UV photon budget.

We participate to the Large-Scale Structure weekly meeting of Thursday and to the Galaxy Clusters Journal Club of Friday. We are involved in the organization of a Focus Week in September 2022, promoted by the Euclid Observational Systematics WP.