Multicomponent and Variable Velocity Galactic Outflow in Cosmological Hydrodynamic Simulations

TL;DR

This paper introduces a new multicomponent, variable velocity galactic outflow model for cosmological simulations, which better matches observed galaxy and intergalactic medium properties than previous models.

Contribution

The paper develops and tests a novel MVV outflow model that accounts for different ISM phases and galaxy mass dependence, improving simulation accuracy.

Findings

IGM temperature remains similar to no-wind runs.

Lower cosmic star formation rates than no-wind, higher than constant wind.

Better agreement with observed IGM metallicity and galaxy mass function.

Abstract

We develop a new ``Multicomponent and Variable Velocity'' (MVV) galactic outflow model for cosmological smoothed particle hydrodynamic (SPH) simulations. The MVV wind model reflects the fact that the wind material can arise from different phases in the interstellar medium (ISM), and the mass-loading factor in the MVV model is a function of galaxy stellar mass. We find that the simulation with the MVV outflow has the following characteristics: (i) the intergalactic medium (IGM) is hardly heated up, and the mean IGM temperature is almost the same as in the no-wind run; (ii) it has lower cosmic star formation rates (SFRs) compared to the no-wind run, but higher SFRs than the constant velocity wind run; (iii) it roughly agrees with the observed IGM metallicity, and roughly follows the observed evolution of Omega(Civ); (iv) the lower mass galaxies have larger mass-loading factors, and the low-mass end of galaxy stellar mass function is flatter than in the previous simulations. Therefore, the MVV outflow model mildly alleviates the problem of too steep galaxy stellar mass function seen in the previous SPH simulations. In summary, the new MVV outflow model shows reasonable agreement with observations, and gives better results than the constant velocity wind model.