Exponential Galaxy Disks from Stellar Scattering

TL;DR

Stellar scattering off orbiting or transient clumps naturally forms exponential surface density and velocity dispersion profiles in galactic disks, independent of initial conditions or complex processes.

Contribution

This work demonstrates that stellar scattering alone can produce exponential galaxy disks without requiring spiral arms, bars, or other traditional mechanisms.

Findings

Exponential profiles form in both surface density and velocity dispersion.

The exponential scale length saturates after rapid initial development.

The outer exponential is mainly composed of scattered stars.

Abstract

Stellar scattering off of orbiting or transient clumps is shown to lead to the formation of exponential profiles in both surface density and velocity dispersion in a two-dimensional non-self gravitating stellar disk with a fixed halo potential. The exponential forms for both nearly-flat rotation curves and near-solid body rotation curves. The exponential does not depend on initial conditions, spiral arms, bars, viscosity, star formation, or strong shear. After a rapid initial development, the exponential saturates to an approximately fixed scale length. The inner exponential in a two-component profile has a break radius comparable to the initial disk radius; the outer exponential is primarily scattered stars.