The fragility of thin discs in galaxies -- I. Building tailored N-body galaxy models

TL;DR

This paper investigates the fragility of thin stellar discs in galaxies through high-resolution N-body simulations, focusing on their stability during intermediate- and low-mass encounters, and develops a detailed dynamical model of FCC 170.

Contribution

It introduces a novel method for constructing self-consistent galaxy models based on detailed kinematic data and demonstrates their stability over billions of years in simulations.

Findings

The galaxy model remains in equilibrium over many Gyr.

Nuclear stellar discs are more susceptible to numerical heating.

Models can realistically represent galaxies in merger studies.

Abstract

Thin stellar discs on both galactic and nuclear, sub-kpc scales are believed to be fragile structures that would be easily destroyed in major mergers. In turn, this makes the age-dating of their stellar populations a useful diagnostics for the assembly history of galaxies. We aim at carefully exploring the fragility of such stellar discs in intermediate- and low- mass encounters, using high-resolution N-body simulations of galaxy models with structural and kinematic properties tailored to actually observed galaxies. As a first but challenging step, we create a dynamical model of FCC 170, a nearly edge-on galaxy in the Fornax cluster with multiple galactic components and including both a galactic scale and nuclear stellar disc (NSD), using detailed kinematic data from the Multi Unit Spectroscopic Explorer and a novel method for constructing distribution function-based self-consistent galaxy models. We then create N-body realisations of this model and demonstrate that it remains in equilibrium and preserves its properties over many Gyr, when evolved with a sufficiently high particle number. However, the NSD is more prone to numerical heating, which gradually increases its thickness by up to 22 per cent in 10 Gyr even in our highest-resolution runs. Nevertheless, these N-body models can serve as realistic representations of actual galaxies in merger simulations.