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Although galactic winds play a critical role in regulating galaxy formation, hydrodynamic cosmological simulations do not resolve the scales that govern the interaction between winds and the ambient circumgalactic medium (CGM). We implement the Physically Evolved Wind (PhEW) model of Huang et al. in the gizmo hydrodynamics code and perform test cosmological simulations with different choices of model parameters and numerical resolution. PhEW adopts an explicit subgrid model that treats each wind particle as a collection of clouds that exchange mass and metals with their surroundings and evaporate by conduction and hydrodynamic instabilities as calibrated on much higher resolution cloud scale simulations. In contrast to a conventional wind algorithm, we find that PhEW results are robust to numerical resolution and implementation details because the small scale interactions are defined by the model itself. Compared to our previous wind simulations with the same resolution, our PhEW simulations are in better agreement with low-redshift galactic stellar mass functions at M* < 1011M⊙ because PhEW particles shed mass to the CGM before escaping low mass haloes. PhEW radically alters the CGM metal distribution because PhEW particles disperse metals to the ambient medium as their clouds dissipate, producing a CGM metallicity distribution that is skewed but unimodal and is similar between cold and hot gas. While the temperature distributions and radial profiles of gaseous haloes are similar in simulations with PhEW and conventional winds, these changes in metal distribution will affect their predicted UV/X-ray properties in absorption and emission.

 

ABSTRACT The propagation and evolution of cold galactic winds in galactic haloes is crucial to galaxy formation models. However, modelling of this process in hydrodynamic simulations of galaxy formation is oversimplified owing to a lack of numerical resolution and often neglects critical physical processes such as hydrodynamic instabilities and thermal conduction. We propose an analytic model, Physically Evolved Winds, that calculates the evolution of individual clouds moving supersonically through a uniform ambient medium. Our model reproduces predictions from very high resolution cloud-crushing simulations that include isotropic thermal conduction over a wide range of physical conditions. We discuss the implementation of this model into cosmological hydrodynamic simulations of galaxy formation as a subgrid prescription to model galactic winds more robustly both physically and numerically. 

ABSTRACT Many phenomenologically successful cosmological simulations employ kinetic winds to model galactic outflows. Yet systematic studies of how variations in kinetic wind scalings might alter observable galaxy properties are rare. Here we employ gadget-3 simulations to study how the baryon cycle, stellar mass function, and other galaxy and CGM predictions vary as a function of the assumed outflow speed and the scaling of the mass-loading factor with velocity dispersion. We design our fiducial model to reproduce the measured wind properties at 25 per cent of the virial radius from the Feedback In Realistic Environments simulations. We find that a strong dependence of η ∼ σ5 in low-mass haloes with $\sigma \lt 106\mathrm{\, km\, s^{-1}}$ is required to match the faint end of the stellar mass functions at $z$ > 1. In addition, faster winds significantly reduce wind recycling and heat more halo gas. Both effects result in less stellar mass growth in massive haloes and impact high ionization absorption in halo gas. We cannot simultaneously match the stellar content at $z$ = 2 and 0 within a single model, suggesting that an additional feedback source such as active galactic nucleus might be required in massive galaxies at lower redshifts, but the amount needed depends strongly on assumptions regarding the outflow properties. We run a 50 $\mathrm{Mpc}\, h^{-1}$, 2 × 5763 simulation with our fiducial parameters and show that it matches a range of star-forming galaxy properties at $z$ ∼ 0–2.