Galactokinetics

TL;DR

This paper introduces a new kinetic theory framework for galactic disk dynamics, simplifying the analysis of fluctuations and transport by dividing potential fluctuations into distinct wavelength regimes, with applications to spiral structure.

Contribution

The paper develops a tractable, regime-based kinetic theory for galactic disks, enabling easier calculation of fluctuations and angular momentum transport.

Findings

Verified formulae with numerical examples

Applied theory to angular momentum transport by spirals

Set groundwork for future spiral structure analysis

Abstract

Galactic disks lie at the heart of many of the most pressing astrophysical puzzles. There are sophisticated kinetic theories that describe some aspects of galaxy disk dynamics, but extracting quantitative predictions from those theories has proven very difficult, meaning they have shed little light on observations/simulations of galaxies. Here, we begin to address this issue by developing a tractable theory describing fluctuations and transport in thin galactic disks. Our main conceptual advance is to split potential fluctuations into asymptotic wavelength regimes relative to orbital guiding radius and epicyclic amplitude (similar to plasma gyrokinetics), and then to treat separately the dynamics in each regime. As an illustration, we apply our results to quasilinear theory, calculating the angular-momentum transport due to a transient spiral. At each stage we verify our formulae with numerical examples. Our approach should simplify many important calculations in galactic disk dynamics. In a follow-up paper, we apply these ideas to the theory of linear spiral structure in stellar disks.