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

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 η ≈ 10 at high redshift, but decrease to η 1 at low redshift. Although lower values of η 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 ≤ 10 12 M to be deficient in baryons compared to the cosmic mean by z = 0.

In-N-Out: The Gas Cycle From Dwarfs to Spiral Galaxies

“…The energy-driven scalings we predict are consistent with those assumed in state-of-the-art simulations that match observed properties of galaxies and the CGM (Dave et al 2013;Ford et al 2014;Genel et al 2014;Vogelsberger et al 2014). They are, however, somewhat different from that predicted by the Feedback in Realistic Galaxies (FIRE) suite of zoom simulations that also self-consistently drive outflows; the FIRE simulations find a shallower dependence for > v 60 circ km s −1 and a steeper dependence for smaller systems (Muratov et al 2015). The amplitude is somewhat lower than typically assumed in cosmological runs; we predict that η is unity for ), whereas such simulations typically assume unity mass loading at , corresponding to mass loading factors a factor of two smaller than typically assumed (e.g., Dave et al 2013).…”

“…We analyze highresolution simulations of 20 spiral and dwarf galaxies that span 2.5 orders of magnitudes in virial mass, all simulated with the same physics and comparable numerical resolution. Our work improves on previous particle tracking analyses that have focused either on low-resolution (non-zoom) simulations of many galaxies (Oppenheimer et al 2010) or on a few simulations of similar-mass galaxies (Brook et al 2012a;Übler et al 2014;Woods et al 2014) and complements non-particletracking studies of galactic winds (Muratov et al 2015).…”

“…This analysis enables us to independently study inflows, outflows, and recycling as a function of galaxy mass, which allows a deeper investigation into the underlying physical processes that govern the baryon cycle. The details of baryon cycling presented here do depend on our methodology for driving outflows and may vary for different choices of physical models (see, e.g., Keller et al 2015;Muratov et al 2015). Nonetheless, our results are of particular interest since our outflow driving model yields a viable match to numerous key observational constraints, as we will show.…”

“…2 ) and a momentum-driven scaling ( -v circ 1 ), respectively (normalized to the data at v circ = 60 km s −1 ). Additionally, the redshift zero fit to the mass loading factor given in Muratov et al (2015) is included as a long-dashed line. Note that differences between how the ejecta was selected here and in Muratov et al (2015) can account for differences in the offset but not in the scaling.…”

“…Additionally, the redshift zero fit to the mass loading factor given in Muratov et al (2015) is included as a long-dashed line. Note that differences between how the ejecta was selected here and in Muratov et al (2015) can account for differences in the offset but not in the scaling. disk is included, the scaling of the mass loading increases to values closer to those assumed in most cosmological simulations.…”