Galactic winds in cosmological simulations of the circumgalactic medium

We explore new observationally constrained subresolution models of galactic outflows and investigate their impact on the circumgalactic medium (CGM) in the redshift range z = 2-4. We perform cosmological hydrodynamic simulations, including star formation, chemical enrichment and four cases of supernovae-driven outflows: no wind (NW), an energy-driven constant velocity wind (CW), a radially varying wind (RVWa) where the outflow velocity has a positive correlation with galactocentric distance (r) and a RVW with additional dependence on halo mass (RVWb). Overall, we find that the outflows expel metal-enriched gas away from galaxies, significantly quench the star formation, reduce the central galactic metallicity and enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy centres are most sensitive to the choice of the wind model for halo masses in the range (109-1011) M⊙. We infer that outflows in the RVWb model are least effective, with results similar to the NW case, except that the CGM is enriched more. Moreover, we find that the models CW and RVWa are similar, both showing the impact of effective winds, with the following notable differences. RVWa causes a greater suppression of star formation rate at z ≤ 5, and has a higher fraction of low-density (δ < 10), warm-hot (104-106 K) gas than in CW. Outflows in CW produce a higher and earlier enrichment of some intergalactic medium phases than in RVWa. By visual inspection, we note that the RVWa model shows galactic discs more pronounced than all the other wind models. We predict that some observational diagnostics are more promising to distinguish between different outflow driving mechanisms in galaxies: ZC of the CGM gas at r ˜ (30-300) h-1 kpc comoving, and C IV fraction of the inner gas at r < (4-5) h-1 kpc comoving.