Exploring the Milky Way with Gaia

Ralph Schoenrich (Oxford)

For Galactic dynamics, the Gaia satellite mission is similar to the invention of the microscope for biology: previously, we had to rely on two-dimensional maps of star counts versus position on the sky. Now, Gaia is measuring parallaxes and proper motions for ~2 billion stars, providing an in-depth view. For >10^7 stars, line-of-sight velocities will complement a full 6D view of the phase space. These great advances in sample size bear a great risk formerly unknown to Galactic astronomy: systematic bias.

I will explain a new statistical distance estimator, which is ~ an order of magnitude more precise and accurate than traditional methods. Applied on Gaia data, this unravels a systematic parallax under-estimate equal to the formal uncertainty for single stars, which we correct.

The map of stellar motions from Gaia reveals an unprecedented wealth of information. Most prominently, we have found a vertical wave perpendicular to the disc plane, which can be related to previous observations in the outer disc. A similar, but much more striking wave-like structure is found in horizontal motions.