How Stellar Feedback Simultaneously Regulates Star Formation and Drives Outflows

By C. Hayward, P. Hopkins. 2015

154 citations recorded by the source corpus.

We present an analytic model for how momentum deposition from stellar feedback simultaneously regulates star formation and drives outflows in a turbulent interstellar medium (ISM). Because the ISM is turbulent, a given patch of ISM exhibits sub-patches with a range of surface densities. The high-density patches are ‘pushed’ by feedback, thereby driving turbulence and self-regulating local star formation. Sufficiently low-density patches, however, are accelerated to above the escape velocity before the region can self-adjust and are thus vented as outflows. When the gas fraction is ≳ 0.3, the ratio of the turbulent velocity dispersion to the circular velocity is sufficiently high that at any given time, of the order of half of the ISM has surface density less than the critical value and thus can be blown out on a dynamical time. The resulting outflows have a mass-loading factor (η≡M_(out)/M_⋆) that is inversely proportional to the gas fraction times the circular velocity. At low gas fractions, the star formation rate needed for local self-regulation, and corresponding turbulent Mach number, declines rapidly; the ISM is ‘smoother’, and it is actually more difficult to drive winds with large mass-loading factors. Crucially, our model predicts that stellar-feedback-driven outflows should be suppressed at z≲1 in M_⋆≳10^(10)M_⊙ galaxies. This mechanism allows massive galaxies to exhibit violent outflows at high redshifts and then ‘shut down’ those outflows at late times, thereby enabling the formation of a smooth, extended thin stellar disc. We provide simple fitting functions for η that should be useful for sub-resolution and semi-analytic models.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/26ae8d88f8861ffe86455cdfe70cb9555727bd00

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Citations in the corpus

The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, background): “…chevance@uni-heidelberg.de posits mass, metals, energy and momentum into the GMCs, eventually leading to their disruption (e.g. Dobbs et al. 2014; Krumholz 2014) and regulating the galaxy-wide star formation rate (SFR; e.g. Ostriker & Shetty 2011; Hayward & Hopkins 2017; Krumholz et al. 2018).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “Initial examination of our FIRE2 runs shows these winds produce galactic outflow rates and covering factors of neutral hydrogen similar to our FIRE-1 simulations, similar to observations at a wide range of galaxy masses (FaucherGiguere et al. 2015; Faucher-Giguère et al. 2016), although this will be”
Black holes on FIRE: stellar feedback limits early feeding of galactic nuclei (2017, background): “…in FIRE simulations, in which early bursty star formation transitions to long-lived gaseous discs with more time-steady star formation in more massive and lower-redshift galaxies (Muratov et al. 2015; Anglés-Alcázar et al. 2017b; Faucher-Giguère 2017; Hayward & Hopkins 2017; Ma et al. 2017a,b).”
The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “ISM effects on Lyα are likely to correlate with galaxy mass and star formation rate (SFR) via dust absorption, neutral hydrogen column density and covering fraction, and outflows (Erb et al. 2014; Erb 2015; Oyarzún et al. 2016; Hayward & Hopkins 2017; Yang et al. 2017).”
A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, background): “…that the star formation rate is set by considerations of force and energy balance within a galactic disc (e.g. Thompson, Quataert & Murray 2005; Ostriker, McKee & Leroy 2010; Hopkins, Quataert & Murray 2011; Ostriker & Shetty 2011; Faucher-Giguère, Quataert & Hopkins 2013; Hayward & Hopkins 2017).”