Description
Galaxy mergers play an important role in galaxy evolution. However, whether and how they shape galaxy properties on multi-Gyr timescales is less well understood. Furthermore, the overall assembly history of a galaxy and its host halo is crucial in determining several of its properties and those of its satellite population. Understanding the causal relationships between assembly and merger histories and galaxy and satellite properties from simulations poses two significant challenges: the large stochastic differences between assembly histories that must be simulated, and the inherent uncertainty in the subgrid prescriptions implemented in the codes. To tackle both, we present results from the PARADIGM project, a suite of zoom-in cosmological hydrodynamical simulations of Milky Way (MW)-mass haloes -- using `genetic modifications' of the initial conditions (ICs) with the GenetIC code to generate controlled alterations to a galaxy's assembly history in a systematic way, and using different simulation codes to understand the impact of different subgrid implementations of galaxy formation. By evolving the same ICs with the VINTERGATAN and IllustrisTNG galaxy formation models, we explore how the overall assembly history impacts the $z=0$ properties of the central galaxy and its satellite populations. We show that the size and kinematics of the central galaxy respond similarly to the altered merger histories in the two codes, with larger mergers resulting in smaller, more spheroidal galaxies. We also consider the response of satellite destruction timescales and the star-formation histories of surviving satellites, finding similar distributions of disruption timescales and quenching times between the two codes.
