The tangled Warp of the Milky Way

Sammanfattning: Context: The Milky Way disc, like the discs of many other spiral galaxies, has been shown to be warped. The growing astrometric data set for stars produced by the Gaia mission allows for more detailed studies of the stellar disc's warp. Aims: We use a full 6-dimensional phase space sample of stars from Gaia DR3 to study the kinematic signature of the Milky Way warp as a function of position in the Galaxy, to better understand the warp's dynamics and its origins. Methods: We build a simple model for the warp's kinematic signature derived from the first Jeans equation and apply it to the stellar sample which stretches a whole half-circle in azimuth around the galaxy and out to 18.5 kpc from the Galactic center. The model is then adjusted to further probe properties of the warp, such as the line of nodes, the warp's precession and the warp shape morphology. Results: We find a single value warp precession rate of 9.87 +- 0.08 km/s/kpc that is in the prograde direction, and line of nodes at 131.45 +- 0.40 degrees in azimuth. In the outer disc, our results show that the line of nodes form a leading spiral with respect to the disc's rotation and that the precession rate decreases with increasing radii. Inspecting the warp amplitude on either side of the Galaxy separately, we find that the disc is asymmetrically warped with a difference of ~40 % at R=15 kpc. Furthermore, we develop a novel approach to study the warp's azimuthal dependence and find that the warp is not as well described in azimuth by a simple sinusoidal shape as previously assumed. Conclusions: The kinematic signature of the Milky Way warp, and its dependence on the galactocentric radius and azimuth, is observable in Gaia DR3. By applying models to the signature we were able to infer that the warp is rapidly precessing around the Galaxy and that the line of nodes is about 50 degrees from that which is often assumed.