Evidence of a vertical kinematic oscillation beyond the Radcliffe wave

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 discovered a kinematic wave in the Galaxy, distinct from the warp, with the amplitude of oscillation depending on the age of the stellar population. We performed 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, setting its origins into question. If a satellite galaxy is indeed responsible for the presence of this kinematic wave, we predict the existence of a vertical velocity dipole that would be expected to form across the disk. The reality of this prediction may be measurable with the upcoming Gaia DR3 and DR4.

The Radcliffe wave as the gas spine of the Orion arm

“…2. The Radcliffe wave shows a vertical sinusoidal undulation (Alves et al 2020), which is not expected in the density wave theory (see Thulasidharan et al 2022). 3.…”

“…If the Radcliffe wave's undulation is somehow related to gas instabilities (Fleck 2020), stellar feedback, or perturbations in the Galactic potential (Antoja et al 2018), one would expect to find more global corrugations in the dust and young stars across the Milky Way. Such structures have been investigated in OB stars (Pantaleoni González et al 2021) and signatures of varying oscillation amplitudes across stars of different ages (5-100 Myr) are present across the disk (Thulasidharan et al 2022). Global corrugations in the dust map of Lallement et al (2022) have also been found, including regions along the Orion arm in the second quadrant and in the Sagittarius-Carina arm in the first and fourth quadrants.…”

“…Two intriguing results emerge from the spatial structure of the Radcliffe wave: One result concerns its coherent undulation about the Galactic plane following a damped sinusoidal pattern, possibly originating from instabilities arising between the Milky Way's disk and halo (Fleck 2020) or due to perturbations caused by the passage of a dwarf galaxy (Thulasidharan et al 2022). The second result concerns the relation between the Radcliffe wave and the Orion (local) arm of the Galaxy.…”

Characterizing the 3D Kinematics of Young Stars in the Radcliffe Wave

“…While Gaia provides 6D phase space information for stars with radial velocities, many works have found it advantageous to convert these quantities into 6D action-angle space coordinates (Sanders & Binney 2016;Beane et al 2018;Trick et al 2019Trick et al , 2021. Actions are conserved quantities that describe a star's motion around the Galactic center; they assume a regular, bound orbit, as well as independence of motion in each coordinate.…”

Parameters of the Radcliffe wave from masers, radio stars and T Tauri stars

“…That is, the vertical velocities have a periodic structure. Thulasidharan et al (2022) studied their vertical velocities using young stars and OSCs located in the circumsolar region with a radius of 3 kpc. These authors came to the conclusion that the Radcliffe wave may be part of a larger periodic process that develops in the disk of the Galaxy.…”