Exploring disc kinematics, substructure & orbits with Milky Way Cepheids.

Classical Cepheids are excellent distance tracers that, when coupled with precise astrometry and line-of-sight velocities from Gaia, allow us to map out the 3D kinematics of the Galactic disc out to at least 16 kpc. In this talk, I will share how thanks to Gaia DR3 and recently improved distances of Milky Way Cepheids, we are able to see the possible influence of the Bar on the outer disc. In particular, we note signatures of a possible resonance (1:1), the imprints of which are seen in the rotation curve of cepheids, as well as in their angular momentum distribution. This also matches well with signatures in action-angle space for red giants.Additionally, by integrating the orbits of all cepheids inside the Galactic warp, we are able to produce an orbital census of young stars in the disc. We find that while most of the cepheids are on disc-like orbits supported by rotation about the Galactic Center, there are candidates that show eccentricities in their orbits (with polar/unbound trajectory). We also find a few candidates for very high velocity stars (Vtot > 450 km/s). In this talk we will summarise our findings in the context of possible interactions between cepheids and other stars/kinematic substructure such as stellar streams, which suggests that cepheids with unusual orbits could be candidate runaway stars themselves.