Impact of Cosmological Satellites on Stellar Discs: Dissecting One Satellite at a Time

TL;DR

This study uses cosmological simulations to show that interactions with massive dark matter subhaloes can induce and sustain various spiral structures and other features in stellar galactic discs, highlighting the importance of satellite impacts.

Contribution

It provides a detailed analysis linking individual subhalo impacts to specific spiral modes, demonstrating how satellite interactions can generate and maintain disc structures over time.

Findings

Massive subhalo impacts induce disc heating and structural features.

Single-armed spirals form after subhalo passages and evolve into two-armed spirals.

Impulsive subhalo interactions are proportional to the torque exerted, influencing spiral strength.

Abstract

Within the standard hierarchical structure formation scenario, Milky Way-mass dark matter haloes have hundreds of dark matter subhaloes with mass $\gtrsim 10^8 \, {\rm M_{\odot}}$. Over the lifetime of a galactic disc a fraction of these may pass close to the central region and interact with the disc. We extract the properties of subhaloes, such as their mass and trajectories, from a realistic cosmological simulation to study their potential effect on stellar discs. We find that massive subhalo impacts can generate disc heating, rings, bars, warps, lopsidedness as wells as spiral structures in the disc. Specifically, strong counter-rotating single-armed spiral structures form each time a massive subhalo passes through the disc. Such single-armed spirals wind up relatively quickly (over $1-2$ Gyrs) and are generally followed by co-rotating two-armed spiral structures that both develop and wind up more slowly. In our simulations self-gravity in the disc is not very strong and these spiral structures are found to be kinematic density waves. We demonstrate that there is a clear link between each spiral mode in the disc and a given subhalo that caused it, and by changing the mass of the subhalo we can modulate the strength of the spirals. Furthermore, we find that the majority of subhaloes interact with the disc impulsively, such that the strength of spirals generated by subhaloes is proportional to the total torque they exert. We conclude that only a handful of encounters with massive subhaloes is sufficient for re-generating and sustaining spiral structures in discs over their entire lifetime.