# Gaia DR3 features of the phase spiral and its possible relation to internal perturbations

**Authors:** Chengdong Li, Arnaud Siebert, Giacomo Monari, Benoit Famaey, Simon Rozier  
**arXiv:** [2303.06393](https://arxiv.org/abs/2303.06393)  
**Date:** 2023-03-11  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.06393v2/

## Key points

- Investigates the phase spiral pattern in the Galaxy and its relation to internal perturbations
- Analyzes data from the Gaia DR3 RVS catalogue, focusing on disc stars
- Finds a two-armed phase spiral pattern within the solar radius, which becomes single-armed outside this region
- Two-armed pattern is characteristic of a breathing mode produced by in-plane non-axisymmetric perturbations
- Uses a realistic analytic model with axisymmetric background potential, rotating bar, and 2-armed spiral arms as perturbations
- Observes prominent spiral pattern in $\langle v_R \rangle$ map on $x-y$ plane and evidence of breathing modes in $\langle v_z \rangle$ map on $x-z$ plane when both bar and spiral arms are present
- No phase-spiral perceptible in $(z,v_z)$ plane, but becomes visible after adding initial vertical perturbation to pseudo stars during simulation
- Toy model demonstrates how time varying non-axisymmetric in-plane perturbation can produce strong two armed phase spiral
- Refines representations of phase spirals along the disc to characterize transition region between one armed and two armed spirals
- Compares findings to test particle simulations with different bar and spiral arm perturbations added to an axisymmetric background model
- Suggests that time varying strong internal perturbation combined with external vertical perturbation could explain transition between two armed and one armed phase spirals around Solar radius
- Discusses future directions for research in this area

## Summary

This paper investigates the phase spiral pattern in the Galaxy and its potential relation to internal perturbations. The authors analyze data from the Gaia DR3 RVS catalogue, specifically focusing on disc stars, to explore how the phase spiral varies with position in the Galaxy. They find a two-armed phase spiral pattern in the local $z-v_z$ plane within the solar radius, which becomes single-armed outside this region. This two-armed pattern is characteristic of a breathing mode that can be produced by in-plane non-axisymmetric perturbations. To further understand the nature of these phase spirals, the authors use a realistic analytic model that includes an axisymmetric background potential, a steadily rotating bar, and 2-armed spiral arms as perturbations. They perform particle test integrations using this model and observe that pseudo stars exhibit a prominent spiral pattern in the $\langle v_R \rangle$ map on the $x-y$ plane. Additionally, they find clear evidence of breathing modes at a few $\rm{kms}^{-1}$ level in the $\langle v_z \rangle$ map on the $x-z$ plane, indicating that these modes are significant when both a bar and spiral arms are present. Interestingly, no phase-spiral is perceptible in the $(z,v_z)$ plane. However, when an initial vertical perturbation is added to all pseudo stars during simulation, one-armed phase spirals become visible after 500 million years and gradually disappear from inside out. Furthermore, as a proof of concept they demonstrate how a toy model of time varying non axisymmetric in plane perturbation with varying amplitude and pattern speed can produce a strong two armed phase spiral. In summary this paper expands on previous research by refining representations of phase spirals along the disc on a finer grid to characterize transition region between one armed and two armed spirals. The authors compare their findings to test particle simulations in galactic potential with different bar and spiral arm perturbations added to an axisymmetric background model. The results suggest that time varying strong internal perturbation combined with external vertical perturbation could potentially explain transition between two armed and one armed phase spirals around Solar radius. The paper concludes by discussing future directions for research in this area overall providing valuable insights into nature of phase spirals in Galaxy and their possible connection to internal perturbations.