# Astronomy seminar: "Reverse Engineering the local Universe"

Constrained simulations (CS) provide a powerful alternative approach to the random-phase Initial Conditions (ICs) cosmological simulations. In this method, galaxy peculiar velocity measurements are used to reconstruct the matter density field and generate a set of ICs whose final outcome closely matches the observed Universe. Hence, while the results obtained with the standard techniques can be compared to the data in a statistical sense only, in a CS we can exploit the constraining potential of the high-precision near-field observations by means of a direct comparison.

After introducing the main ideas and algorithms behind the CS technique, its applications on both large (5 to 100 Mpc) and small (sub-Mpc) scales will be discussed. I will describe the results of a recent Nature Astronomy publication where these simulations have been used to reconstruct the quasi-linear matter distribution and determine for the first time the non-linear bias factor on scales below 20 Mpc. I will then show how these results can be used to link the anisotropies of the Ultra High Energy Cosmic Rays (UHECR) spectrum (measured by the Pierre Auger Collaboration) to the large scale structure.

The last part of this seminar will show some of the small-scale applications of the method introducing the Local Group Factory, a numerical pipeline designed to study Local Group (LG) lookalikes within a realistic environment, akin to the observed one. I will show how this can be used to shed light on poorly-constrained LG properties such as its mass and the tangential velocity of M31 as well as constrain

alternative cosmological models. I will conclude introducing future applications of the pipeline such as the HESTIA project, a suite of hydrodynamical zoom simulations of the Local Group run with the AREPO code.