Galactic winds - How to launch galactic outflows in typical Lyman-break galaxies

TL;DR

This study uses hydrodynamical simulations to explore how supernova-driven superbubbles can launch bipolar galactic outflows in Lyman-break galaxies, highlighting the roles of halo pressure and superbubble size.

Contribution

It demonstrates the conditions under which superbubbles lead to galactic outflows and how halo pressure can suppress these winds, providing insights into feedback processes in LBGs.

Findings

Superbubbles are more effective at driving outflows when larger in size.

Halo gas pressure can quench galactic winds.

Outflows are associated with superbubbles exceeding a critical star formation density.

Abstract

We perform hydrodynamical simulations of a young galactic disc embedded in a hot gaseous halo using parameters typical for Lyman break galaxies (LBGs). We take into account the (static) gravitational potentials due to a dark matter halo, a stellar bulge and a disc of stars and gas. Star formation is treated by a local Kennicutt-Schmidt law. We simplify the structure of the interstellar medium by restricting the computational domain to a 25th of the full azimuthal angle, effectively assuming large-scale axisymmetry and neglecting any effects of spiral structure, and focus on the large-scale ISM drivers, the superbubbles. Supernovae are triggered randomly and have preset event sizes of several tens to hundreds. We further investigate different halo gas pressures and energy injection methods. Many of our simulated galaxies, but not all, develop bipolar outflows. We characterise the strength of the outflow by mass and energy outflow rates, and investigate the effect of changes to the details of the model. We find that supernovae are more effective if comprised into larger superbubbles. The weight and the pressure of the halo gas is able to quench galactic outflows. The wind emerges from a series of superbubbles in regions where a critical star formation density is exceeded. The superbubbles expand into the gaseous halo at slightly supersonic speed, producing radiative shock waves with similar characteristics as the absorptions systems observed around LBGs.