# Galactic seismology: joint evolution of stellar and gaseous disc corrugations triggered by a crossing satellite

**Authors:** Thor Tepper-Garcia, Joss Bland-Hawthorn, Ken Freeman  
**arXiv:** [2204.12096](https://arxiv.org/abs/2204.12096)  
**Date:** 2022-04-26  
**Summary page:** https://www.summarizepaper.com/en/paper/2204.12096v1/

## Key points

- Growing evidence for wave-like corrugations in the Milky Way and nearby disc galaxies
- Corrugations observed as displacement of interstellar medium in terms of vertical distance or velocity around midplane
- Similar patterns detected in stellar disc of Milky Way
- Study aims to investigate how these waves are triggered by passing satellite
- High-resolution simulations used to study setup and evolution of corrugations in stellar and gaseous discs
- Gas corrugations initially follow stellar corrugations, but separate and evolve independently after a few rotation periods (500-700 million years)
- Spatial and kinematic amplitudes of corrugations gradually dampen over time, with gaseous corrugation settling faster (around 800 million years) compared to stellar corrugation (around 1 billion years)
- Damping of stellar corrugations attributed to incomplete phase mixing, while gaseous corrugations naturally dissipate due to their dissipative nature
- Difference in damping between stellar and gaseous waves provides insights into dating this phenomenon
- Study contributes to understanding galactic seismology and dynamics of disc galaxies

## Summary

In recent years, there has been growing evidence for the presence of wave-like corrugations in the Milky Way and nearby disc galaxies. These corrugations were initially observed as a displacement of the interstellar medium in terms of vertical distance or velocity around the midplane. More recently, similar patterns have been detected in the stellar disc of the Milky Way. In this study, conducted by Thor Tepper-Garcia, Joss Bland-Hawthorn, and Ken Freeman, the researchers aim to investigate how these vertical waves are triggered by a passing satellite. To do so, they utilize high-resolution N-body/hydrodynamical simulations to study the setup and evolution of these corrugations in both the stellar and gaseous discs. The findings reveal that gas corrugations follow stellar corrugations initially, meaning they are in phase with each other. However, after a few rotation periods (approximately 500-700 million years), these distinct waves separate and evolve independently. The spatial and kinematic amplitudes of the corrugations gradually dampen over time, with the gaseous corrugation settling at a faster rate (around 800 million years) compared to the stellar corrugation (around 1 billion years). Interestingly, while the vertical energy of individual disc stars remains fairly constant throughout the galaxy's evolution, there is a difference in damping between stellar and gaseous corrugations. This discrepancy arises because corrugations are an emergent phenomenon supported by collective ordered motions of co-spatial ensembles of stars. The damping of stellar corrugations can be attributed to incomplete phase mixing whereas gaseous corrugations naturally dissipate due to their dissipative nature. The researchers suggest that studying the degree of correlation between stellar and gaseous waves may provide insights into dating this phenomenon. By understanding how these vertical waves are triggered by passing satellites and how they evolve jointly in both stellar and gaseous discs, this study contributes to our understanding of galactic seismology and dynamics of disc galaxies.