Warp, Waves, and Wrinkles in the Milky Way

Understand

We derive unbiased distance estimates for the Gaia-TGAS dataset by correcting for the bias due to the distance dependence of the selection function, which we measure directly from the data.

• From these distances and proper motions, we estimate the vertical and azimuthal velocities, $W$ and $V_\phi$, and angular momentum $L_z$ for stars in the Galactic centre and anti-centre directions.
• The resulting mean vertical motion $\overline{W}$ shows a linear increase with both $V_\phi$ and $L_z$ at $10 \sigma$ significance.
• Such a trend is expected from and consistent with the known Galactic warp.