Understanding Galaxy Outflows as the Product of Unstable Turbulent Support

TL;DR

This paper investigates how unstable turbulent support in the interstellar medium leads to hot gas outflows in galaxies with high gas surface densities, affecting galaxy evolution and star formation.

Contribution

It introduces a model linking turbulent velocities to gas instability and outflow formation, highlighting the role of turbulence in galaxy feedback mechanisms.

Findings

Hot outflows form in galaxies with gas surface density >50 M_sun/pc^2.

In galaxies with escape velocity >200 km/s, outflow sonic points are inside the cold gas region.

Energy balance fails in turbulent media with surface density >10^5 M_sun/pc^2.

Abstract

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 approximately 35 km/s, 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 approximately 50 solar masses/pc^2 corresponding to a star formation rate per unit area of 0.1$ solar masses/yr/kpc^2. For galaxies with escape velocities above 200 km/s, 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 approximately 10^5 solar masses/pc^2.