Gas accretion and galactic fountain flows in the Auriga cosmological simulations: angular momentum and metal re-distribution

Until recently, cosmological hydrodynamical simulations of the formation of Milky Way mass galaxies failed to produce disc-dominated spiral galaxies. This is now possible thanks to the inclusion of strong feedback and improved resolution and codes. I present the Auriga project - one of the largest, highest-resolution suites of magneto-hydrodynamic zoom-in simulations for Milky Way formation, which include a comprehensive galaxy formation model (including stellar and AGN feedback and magnetic fields), validated in large box simulations. The simulations reproduce a number of observed scaling relations, and provide a valuable look into the origin and formation of discs over cosmic time. In this talk, I quantify how the material that forms stars by redshift zero is accreted onto the galaxy, and find that about half originates from subhalo/satellite systems of a range of masses, via processes such as ram-pressure stripping and wind-accretion. The other half accretes smoothly from the Inter-Galactic Medium (IGM), most of which is subsequently wind-recycled several times in a fountain flow. I demonstrate that fountain flows produce flat star formation histories and acquire angular momentum for the disc via mixing low-angular momentum, wind-recycled gas with high-angular momentum gas in the Circum-Galactic Medium (CGM). I discuss the effects of mergers on this evolution, and the implications for the metals distributed throughout the galaxy.