The Impact of Wind Scalings on Stellar Growth and the Baryon Cycle in Cosmological Simulations

TL;DR

This study uses cosmological simulations to explore how different wind scalings affect galaxy growth, the baryon cycle, and observable properties, highlighting the sensitivity of galaxy formation outcomes to feedback models.

Contribution

It systematically investigates the impact of wind speed and mass loading scalings on galaxy evolution, revealing the need for additional feedback mechanisms like AGN in massive galaxies.

Findings

Strong mass loading dependence ($eta o \sigma^5$) is needed for low-mass halos.

Faster winds reduce recycling and halo gas heating, affecting stellar mass growth.

Simulation results are highly sensitive to feedback implementation details.

Abstract

Many phenomenologically successful cosmological galaxy formation simulations employ kinetic winds to model galactic outflows, a crucial ingredient in obtaining predictions that agree with various observations. 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 $v_w$ and the scaling of the mass loading factor $\eta$ with velocity dispersion $\sigma$. We design our fiducial model to reproduce the measured wind properties at 25% of the virial radius from the Feedback In Realistic Environments (FIRE) simulations. We find that a strong dependence of $\eta \sim \sigma^5$ in low mass haloes with $\sigma < 106\ \mathrm{km\ s^{-1}}$ is required to match the faint end of the stellar mass functions at $z > 1$. The wind speed also has a major impact, with faster winds significantly reducing wind recycling and heating 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 $z=0$ within a single model, suggesting that an additional feedback source such as AGN 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 $\mathrm{Mpc/h}$, $2\times576^3$ simulation with our fiducial parameters and show that it matches a range of star-forming galaxy properties at $z\sim0-2$. In closing, the results from simulations of galaxy formation are much more sensitive to small changes in the feedback implementation than to the hydrodynamic technique.