Abstract
We study galaxy super-winds driven in major mergers, using pc-resolution simulations with detailed models for stellar feedback that can self-consistently follow the formation/destruction of GMCs and generation of winds. The models include molecular cooling, star formation at high densities in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind mass-loading efficiency (outflow rate divided by SFR) is similar to that in isolated galaxy counterparts of each merger: it depends more on global galaxy properties (mass, size, escape velocity) than on the dynamical state of the merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up complex morphologies with overlapping, differently-oriented bubbles/shells at a range of radii. The winds have complex velocity and phase structure, with material at a range of speeds up to ~1000 km/s, and a mix of molecular, ionized, and hot gas that depends on galaxy properties and different feedback mechanisms. These simulations resolve a problem in some 'sub-grid' models, where simple wind prescriptions can dramatically suppress merger-induced starbursts. But despite large mass-loading factors (>~10) in the winds, the peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration does not act equally, so cold dense gas can still lose angular momentum and form stars, while blowing out gas that would not have participated in the starburst in the first place. Considerable wind material is not unbound, and falls back on the disk at later times post-merger, leading to higher post-starburst SFRs in the presence of stellar feedback. This may require AGN feedback to explain galaxy quenching.
Highlights
It is well established that feedback from stars is a key component of galaxy formation models
In Hopkins, Quataert & Murray (2012b, Paper III), we show that these same models of stellar feedback predict the elusive winds invoked in almost all galaxy formation models; the combination of multiple feedback mechanisms is critical to give rise to massive, multiphase winds having a broad distribution of velocities, with material both stirred in local fountains and unbound from the disc
We focus on simple, global properties and compare them to those obtained from previous generations of simulations which did not follow these processes explicitly but instead adopted a simplified ‘effective equation of state’ subgrid model of the interstellar medium (ISM)
Summary
It is well established that feedback from stars is a key component of galaxy formation models. 2012; Teyssier et al 2013) This should not be surprising: feedback processes other than SNe are critical for suppressing SF in dense gas; these include protostellar jets, H II photoionization, stellar winds and radiation pressure from young stars. This conclusion implies that (not surprisingly) an accurate treatment of galactic winds requires a more realistic treatment of the stellar feedback processes that maintain the multiphase structure of the ISM of galaxies Motivated by these problems, in Hopkins, Quataert & Murray (2011, Paper I) and Hopkins, Quataert & Murray (2012a, Paper II), we developed a new set of numerical models to follow feedback on small scales in giant molecular clouds (GMCs) and star-forming regions, in simulations with pc-scale resolution.. We further investigate the phase structure and generation of galactic superwinds in these models, and how they relate to merger dynamics and SF histories
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