Diffuse gas properties and stellar metallicities in cosmological simulations of disc galaxy formation

We analyse the properties of the circumgalactic medium and the metal content of the stars comprising the central galaxy in eight hydrodynamical ‘zoom-in’ simulations of disc galaxy formation. We use these properties as a benchmark for our model of galaxy formation physics implemented in the moving-mesh code arepo, which succeeds in forming quite realistic late-type spirals in the set of ‘Aquarius’ initial conditions of Milky-Way-sized haloes. Galactic winds significantly influence the morphology of the circumgalactic medium and induce bipolar features in the distribution of heavy elements. They also affect the thermodynamic properties of the circumgalactic gas by supplying an energy input that sustains its radiative losses. Although a significant fraction of the heavy elements are transferred from the central galaxy to the halo, and even beyond the virial radius, enough metals are retained by stars to yield a peak in their metallicity distributions at about Z⊙. All our default runs overestimate the stellar [O/Fe] ratio, an effect that we demonstrate can be rectified by an increase of the adopted Type Ia supernova rate. Nevertheless, the models have difficulty in producing stellar metallicity gradients of the same strength as observed in the Milky Way.