Simulating Supersonic Turbulence in Galaxy Outflows

TL;DR

This paper introduces a new simulation approach for galaxy outflows driven by supersonic turbulence, capturing complex gas dynamics and cooling effects in dwarf galaxies like NGC 1569.

Contribution

It develops a subgrid turbulence model integrated with adaptive mesh simulations, enabling realistic representation of supernova-driven turbulence and outflows in starburst galaxies.

Findings

Supersonic turbulence drives large-scale outflows avoiding dense regions.

Cooling instability creates long-lived hot gas pockets around OB associations.

Turbulent mixing leads to chaotic bubble and filament structures.

Abstract

We present three-dimensional, adaptive mesh simulations of dwarf galaxy out- flows driven by supersonic turbulence. Here we develop a subgrid model to track not only the thermal and bulk velocities of the gas, but also its turbulent velocities and length scales. This allows us to deposit energy from supernovae directly into supersonic turbulence, which acts on scales much larger than a particle mean free path, but much smaller than resolved large-scale flows. Unlike previous approaches, we are able to simulate a starbursting galaxy modeled after NGC 1569, with realistic radiative cooling throughout the simulation. Pockets of hot, diffuse gas around individual OB associations sweep up thick shells of material that persist for long times due to the cooling instability. The overlapping of high-pressure, rarefied regions leads to a collective central outflow that escapes the galaxy by eating away at the exterior gas through turbulent mixing, rather than gathering it into a thin, unstable shell. Supersonic, turbulent gas naturally avoids dense regions where turbulence decays quickly and cooling times are short, and this further enhances density contrasts throughout the galaxy- leading to a complex, chaotic distribution of bubbles, loops and filaments as observed in NGC 1569 and other outflowing starbursts.