Tracing the Galactic disk from the kinematics of Gaia Cepheids

Abstract: Classical Cepheids (CCs) are excellent tracers for understanding the structure of the Milky Way disk. The latest Gaia Data Release 3 provides a large number of line-of-sight velocity information for Galactic CCs, offering an opportunity for studying the kinematics of the Milky Way. We determine the three-dimensional velocities of 2057 CCs relative to the Galactic center. From the projections of the 3D velocities onto the XY plane of the Galactic disk, we find that $V_{R}$ and $V_{\phi}$ velocities of the northern and southern warp (directions with highest amplitude) are different. This phenomenon may be related to the warp precession or the asymmetry of the warp structure. By investigating the kinematic warp model, we find that the vertical velocity of CCs is more suitable for constraining the warp precession rate than the line of nodes angles. Our results suggest that CCs at $12-14$ kpc are the best sample for determining the Galactic warp precession rate. Based on the spatial structure parameters of Cepheid warp from Chen et al (arXiv:1902.00998), we determine a warp precession rate of $\omega = 4.9\pm1.6$ km s$^{-1}$ kpc$^{-1}$ at 13 kpc, which supports a low precession rate in the warp model. In the future, more kinematic information on CCs will help to better constrain the structure and evolution of the Milky Way.