Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback

TL;DR

This paper analyzes galaxy-scale gaseous outflows in FIRE cosmological simulations, revealing how star formation bursts drive winds at high redshift and how galaxy evolution affects outflow properties and baryon content.

Contribution

It provides detailed insights into the evolution of galactic winds and outflows across cosmic time using high-resolution simulations with explicit stellar feedback.

Findings

High redshift galaxies have strong, burst-driven outflows with high mass-loading factors.

Low redshift massive galaxies develop stable disks with suppressed outflows.

Many ejected gases are retained in the circumgalactic medium, but some are lost permanently.

Abstract

We present an analysis of the galaxy-scale gaseous outflows from the FIRE (Feedback in Realistic Environments) simulations. This suite of hydrodynamic cosmological zoom simulations resolves formation of star-forming giant molecular clouds to $z=0$, and features an explicit stellar feedback model on small scales. Our simulations reveal that high redshift galaxies undergo bursts of star formation followed by powerful gusts of galactic outflows that eject much of the ISM and temporarily suppress star formation. At low redshift, however, sufficiently massive galaxies corresponding to L*-progenitors develop stable disks and switch into a continuous and quiescent mode of star formation that does not drive outflows far into the halo. Mass-loading factors for winds in L*-progenitors are $\eta \approx 10$ at high redshift, but decrease to $\eta \ll 1$ at low redshift. Although lower values of $\eta$ are expected as halos grow in mass over time, we show that the strong suppression of outflows with decreasing redshift cannot be explained by mass evolution alone. Circumgalactic outflow velocities are variable and broadly distributed, but typically range between one and three times the circular velocity of the halo. Much of the ejected material builds a reservoir of enriched gas within the circumgalactic medium, some of which could be later recycled to fuel further star formation. However, a fraction of the gas that leaves the virial radius through galactic winds is never regained, causing most halos with mass $M_h \le 10^{12} M_{\odot}$ to be deficient in baryons compared to the cosmic mean by $z=0$.