Understanding galaxy outflows as the product of unstable turbulent support

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16 Scopus citations


The interstellar medium is a multiphase gas in which turbulent support is as important as thermal pressure. Sustaining this configuration requires both continuous turbulent stirring and continuous radiative cooling to match the decay of turbulent energy. While this equilibrium can persist for small turbulent velocities, if the one-dimensional velocity dispersion is larger than ≈35 km s-1, the gas moves into an unstable regime that leads to rapid heating. I study the implications of this turbulent runaway, showing that it causes a hot gas outflow to form in all galaxies with a gas surface density above ≈50 M pc-2, corresponding to a star formation rate per unit area of ≈0.1 M yr-1 kpc-2. For galaxies with v esc ≳ 200 km s-1, the sonic point of this hot outflow should lie interior to the region containing cold gas and stars, while for galaxies with smaller escape velocities, the sonic point should lie outside this region. This leads to efficient cold cloud acceleration in higher mass galaxies, while in lower mass galaxies, clouds may be ejected by random turbulent motions rather than accelerated by the wind. Finally, I show that energy balance cannot be achieved at all for turbulent media above a surface density of ≈105 M pc-2.

Original languageEnglish (US)
Article numberL31
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Feb 1 2013


  • ISM: jets and outflows
  • ISM: structure
  • galaxies: starburst

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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