Principles of supernova-driven winds

TL;DR

This paper develops an analytic model linking supernova feedback assumptions to galaxy baryon content, tests these against simulations, and finds that supernova winds alone may not explain baryon loss in low-mass galaxies.

Contribution

It introduces a comprehensive analytic framework that incorporates velocity distributions and combines energy and momentum constraints, improving understanding of supernova-driven winds.

Findings

Analytic predictions align with observed baryon fractions in intermediate-mass galaxies.

Simulations show different wind-driving mechanisms dominate depending on galaxy mass and resolution.

Current supernova wind models may be insufficient to explain baryon loss in low-mass systems.

Abstract

The formation of galaxies is regulated by a balance between the supply of gas and the rate at which it is ejected. Traditional explanations of gas ejection equate the energy required to escape the galaxy or host halo to an estimate for the energy yield from supernovae. This yield is usually assumed to be a constant fraction of the total available from the supernova, or is derived from the assumption of a consistent momentum yield. By applying these ideas in the context of a cold dark matter cosmogony, we derive a 1st-order analytic connection between these working assumptions and the expected relationship between baryon content and galaxy circular velocity, and find that these quick predictions straddle recent observational estimates. To examine the premises behind these theories in more detail, we then explore their applicability to a set of gasdynamical simulations of idealised galaxies. We show that different premises dominate to differing degrees in the simulated outflow, depending on the mass of the system and the resolution with which it is simulated. Using this study to anticipate the emergent behaviour at arbitrarily high resolution, we motivate more comprehensive analytic model which allows for the range of velocities with which the gas may exit the system, and incorporates both momentum and energy-based constraints on the outflow. Using a trial exit velocity distribution, this is shown to be compatible with the observed baryon fractions in intermediate-mass systems, but implies that current estimates for low-mass systems can not be solely accounted for by supernova winds under commonly-held assumptions.