Asano et al. (2024)

Abstract

Theoretical models of spiral arms suggest that the spiral arms provoke a vertical bulk motion in disk stars. By analysing the breathing motion, a coherent symmetric vertical motion around the mid-plane of the Milky Way disc, with the Gaia data, we found that a compressing breathing motion presents along the Local arm. On the other hand, with the isolated $N$-body model, we found that the transient and dynamic spiral arms induce compressing breathing motions when the arms are in the growth phase. The observed clear alignment of the compressing breathing motion with the Local arm is similar to what is seen in the growth phase of the simulated spiral arms. Hence, this result suggests that the Local arm’s compressing breathing motion can be explained by the Local arm being in the growth phase of a transient and dynamic spiral arm.