Stellar scattering and the formation of exponential discs in self-gravitating systems

TL;DR

This study demonstrates through N-body simulations that stellar scattering by massive clumps can rapidly form exponential galactic discs, with the process influenced by clump mass and disc stability, leading to specific dynamical and structural changes.

Contribution

It provides the first detailed simulation evidence that stellar scattering by massive clumps can produce exponential discs quickly, supporting analytic theories of disc formation.

Findings

Exponential discs form within 1 Gyr due to scattering.

Disc thickening and velocity dispersion increase observed.

Stellar orbits become more eccentric over time.

Abstract

We show, using the N-body code GADGET-2, that stellar scattering by massive clumps can produce exponential discs, and the effectiveness of the process depends on the mass of scattering centres, as well as the stability of the galactic disc. Heavy, dense scattering centres in a less stable disc generate an exponential profile quickly, with a timescale shorter than 1 Gyr. The profile evolution due to scattering can make a near-exponential disc under various initial stellar distributions. This result supports analytic theories that predict the scattering processes always favour the zero entropy gradient solution to the Jeans/Poisson equations, whose profile is a near-exponential. Profile changes are accompanied by disc thickening, and a power-law increase in stellar velocity dispersion in both vertical and radial directions is also observed through the evolution. Close encounters between stars and clumps can produce abrupt changes in stellar orbits and shift stars radially. These events can make trajectories more eccentric, but many leave eccentricities little changed. On average, orbital eccentricities of stars increase moderately with time.