Feedback and recycled wind accretion: assembling the z= 0 galaxy mass function

Abstract

We analyse cosmological hydrodynamic simulations that include theoretically and observationally motivated prescriptions for galactic outflows. If these simulated winds accurately represent winds in the real Universe, then material previously ejected in winds provides the dominant source of gas infall for new star formation at redshifts z < 1. This recycled wind accretion, or wind mode, provides a third physically distinct accretion channel in addition to the ‘hot’ and ‘cold’ modes emphasized in recent theoretical studies. The recycling time of wind material (trec) is shorter in higher mass systems owing to the interaction between outflows and the increasingly higher gas densities in and around higher mass haloes. This differential recycling plays a central role in shaping the present‐day galaxy stellar mass function (GSMF), because declining trec leads to increasing wind mode galaxy growth in more massive haloes. For the three feedback models explored, the wind mode dominates above a threshold mass that primarily depends on wind velocity; the shape of the GSMF therefore can be directly traced back to the feedback prescription used. If we remove all particles that were ever ejected in a wind, then the predicted GSMFs are much steeper than observed. In this case, galaxy masses are suppressed both by the ejection of gas from galaxies and by the hydrodynamic heating of their surroundings, which reduces subsequent infall. With wind recycling included, the simulation that incorporates our favoured momentum‐driven wind scalings reproduces the observed GSMF for stellar masses 109 M⊙≤M≤ 5 × 1010 M⊙. At higher masses, wind recycling leads to excessive galaxy masses and star formation rates relative to observations. In these massive systems, some quenching mechanism must suppress not only the direct accretion from the primordial intergalactic medium but the re‐accretion of gas ejected from star‐forming galaxies. In short, as has long been anticipated, the form of the GSMF is governed by outflows; the unexpected twist here for our simulated winds is that it is not primarily the ejection of material but how the ejected material is re‐accreted that governs the GSMF.

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

“…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 simulations predict that the recycling time for momentumdriven wind scales roughly inversely with the halo mass for moderate-sized star-forming galaxies (Oppenheimer & Davé 2008;Oppenheimer et al 2010), and some semianalytic models have found that similar scalings are best able to reproduce various observations, such as the stellar mass function (Henriques et al 2013). Here we directly track the recycling time in our simulations as a function of halo mass.…”

“…Previous theoretical work has shown that the recycling of gas through reaccretion back onto the disk is key to reproducing observed stellar masses (Oppenheimer et al 2010;Henriques et al 2013), metal enrichment , and mass distributions (Brook et al 2012a). In this section, we quantify reaccretion, or wind recycling, as a function of halo mass, as well as the distribution of recycling times.…”

“…This so-called wind recycling adds to the pristine accretion from the IGM and to the accretion of gas already bound in galaxies (i.e., mergers). The recycling of previously ejected wind material can be a key factor in setting the galaxy stellar mass function (e.g., Oppenheimer et al 2010;Bower et al 2012). It is also thought that fountaining gas gains angular momentum through interactions within the halo environment before being reaccreted (Marasco et al 2012), which further shifts the angular momentum distribution of the disk baryons to higher values (Brook et al 2012a).…”

Dusty star-forming galaxies at high redshift

“…Bouché et al, 2010;Dutton et al, 2010;Lagos et al, 2011;Davé et al, 2012). In galaxy formation theory, the baryonic gas fraction is set by a balance between gas accretion from the intergalactic medium (IGM), and the removal of gas by star formation and galactic outflows (with small perturbations from stellar mass loss and recycled gas outflows Oppenheimer et al, 2010). At higher redshifts, the baryonic inflow rate, which scales strongly with redshift (e.g.…”