Exponential Disks from Stellar Scattering: III. Stochastic Models

TL;DR

This paper demonstrates that exponential stellar disk profiles naturally emerge from stochastic scattering processes with a slight inward bias, explaining their ubiquity in galaxies.

Contribution

It provides a fundamental mathematical explanation for exponential profiles resulting from biased stellar scattering in galaxy disks.

Findings

Exponentials arise from biased stochastic scattering.

Double exponentials occur when bias varies with radius.

This mechanism explains the commonality of exponential profiles in galaxies.

Abstract

Stellar scattering off irregularities in a galaxy disk has been shown to make an exponential radial profile, but no fundamental reason for this has been suggested. Here we show that exponentials are mathematically expected from random scattering in a disk when there is a slight inward bias in the scattering probability. Such a bias was present in our previous scattering experiments that formed exponential profiles. Double exponentials can arise when the bias varies with radius. This is a fundamental property of scattering and may explain why piece-wise exponential profiles are ubiquitous in galaxies, even after minor mergers and other disruptive events.