Evidence of a vertical kinematic oscillation beyond the Radcliffe Wave

TL;DR

This paper identifies a vertical kinematic oscillation beyond the Radcliffe Wave, suggesting it may be caused by external perturbations like a satellite galaxy, with implications for understanding galactic dynamics.

Contribution

It provides the first evidence of a distinct vertical kinematic wave beyond the Radcliffe Wave and explores its possible origin from external perturbations.

Findings

Discovery of a vertical kinematic wave beyond the Radcliffe Wave.

The amplitude of oscillation varies with stellar population age.

The observed wave's properties challenge a simple external perturbation explanation.

Abstract

The Radcliffe Wave (RW) is a recently discovered sinusoidal vertical feature of dense gas in the proximity of the Sun. In the disk plane, it is aligned with the Local Arm. However, the origin of its vertical undulation is still unknown. This study constrains the kinematics of the RW, using young stars and open clusters as tracers, and explores the possibility of this oscillation being part of a more extended vertical mode. We study the median vertical velocity trends of the young stars and clusters along with the RW and extend it further to the region beyond it. We discover a kinematic wave in the Galaxy, distinct from the warp, with the amplitude of oscillation depending on the age of the stellar population. We perform a similar analysis in the N-body simulation of a satellite as massive as the Sagittarius dwarf galaxy impacting the galactic disk. When projected in the plane, the spiral density wave induced by the satellite impact is aligned with the RW, suggesting that both may be the response of the disk to an external perturbation. However, the observed kinematic wave is misaligned. It appears as a kinematic wave travelling radially, winding up faster than the density wave matched by the RW, questioning its origin. If a satellite galaxy is responsible for this kinematic wave, we predict the existence of a vertical velocity dipole that should form across the disk and this may be measurable with the upcoming Gaia DR3 and DR4.