Gas and stellar spiral structures in tidally perturbed disc galaxies

TL;DR

This study uses 3D simulations to compare gas and stellar spiral structures in tidally perturbed galaxies, revealing minimal morphological differences but identifying key features like gas spurring and radial migration, and establishing a low-mass threshold for spiral generation.

Contribution

It provides a detailed comparison of gas and stellar spiral arms in galaxy interactions and determines the minimal companion mass needed to induce spiral structures.

Findings

Gas and stellar arms have similar morphology and pattern speeds.

Minor offsets and spurring features are observed in gaseous arms.

A companion mass of about 10^9 solar masses can generate spiral structures.

Abstract

Tidal interactions between disc galaxies and low mass companions are an established method for generating galactic spiral features. In this work we present a study of the structure and dynamics of spiral arms driven in interactions between disc galaxies and perturbing companions in 3-D N-body/smoothed hydrodynamical numerical simulations. Our specific aims are to characterize any differences between structures formed in the gas and stars from a purely hydrodynamical and gravitational perspective, and to find a limiting case for spiral structure generation. Through analysis of a number of different interacting cases, we find that there is very little difference between arm morphology, pitch angles and pattern speeds between the two media. The main differences are a minor offset between gas and stellar arms, clear spurring features in gaseous arms, and different radial migration of material in the stronger interacting cases. We investigate the minimum mass of a companion required to drive spiral structure in a galactic disc, finding the limiting spiral generation cases with companion masses of the order $1\times10^9M_\odot$, equivalent to only 4% of the stellar disc mass, or 0.5% of the total galactic mass of a Milky Way analogue.