The role of cold flows and reservoirs in galaxy formation with strong feedback

Abstract

We examine gas accretion and subsequent star formation in representative galaxies from the McMaster Unbiased Galaxy Simulations ). Accreted gas is bimodal with a natural temperature division at 10 5 K, near the peak of the cooling curve. Cold-mode accretion dominates inflows at early times, creating a peak in total accretion at redshift z=2-4 and declining exponentially below z∼2. Hot-mode accretion peaks near z=1-2 and declines gradually. Hot-mode exceeds cold-mode accretion at z∼1.8 for all four galaxies rather than when the galaxy reaches a characteristic mass. Cold-mode accretion can fuel immediate star formation, while hot-mode accretion preferentially builds a large, hot gas reservoir in the halo. Late-time star formation relies on reservoir gas accreted 2-8 Gyr prior. Thus, the reservoir allows the star formation rate to surpass the current overall gas accretion rate. Stellar feedback cycles gas from the interstellar medium back into the hot reservoir. Stronger feedback results in more gas cycling, gas removal in a galactic outflow and less star formation overall, enabling simulations to match the observed star formation history. For lower mass galaxies in particular, strong feedback can delay the star formation peak to z=1-2 from the accretion peak at z=2-4.

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

“…Christensen et al (2014b) showed that the blastwave feedback model results in a much more efficient removal of gas when combined with a highly resolved ISM that included the cold molecular phase, as used here. This change in the efficiency is also apparent by comparing the results here to those in Woods et al (2014), which examined a blastwave feedback model using lowerresolution simulations and without a molecular hydrogen model. In Woods et al (2014), the blastwave feedback model was unable to remove baryons from…”

“…This change in the efficiency is also apparent by comparing the results here to those in Woods et al (2014), which examined a blastwave feedback model using lowerresolution simulations and without a molecular hydrogen model. In Woods et al (2014), the blastwave feedback model was unable to remove baryons from…”

“…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).…”

Cosmological galaxy evolution with superbubble feedback – I. Realistic galaxies with moderate feedback

“…We selected an intermediate-mass halo, g1536, allowing us to compare to a number of other studies that have examined this particular halo (e.g. Stinson et al 2013;Woods et al 2014). At z = 0 this halo has a virial mass of 8 × 10 11 M⊙ and a spin parameter of 0.017.…”

The impact of feedback on cosmological gas accretion

“…Murante et al (2012) used a thermal supernova feedback scheme, and found that additional heating of cold inflow due to this feedback gave rise to a significant accretion rate of intermediate temperature gas. Most recently, Woods et al (2014) includes a combined delayed cooling supernova and early stellar feedback model, finding that overall gas accretion rates did not change with strong feedback, while the balance between cold and hot components did. Finally, Ubler et al (2014) implements a hybrid thermal/kinetic stellar feedback scheme and finds strong outflows generate substantially higher raw accretion rates, and that recycled material dominates galactic gas accretion at z < 1.…”