a clear, flat map of stellar motion with Gaia

Mappting the phase space of Milky Way has been a difficult task. Two major challenges are the high dimensionality (6D, or 4D when simplified) and observational bias (we observe much more close-by stars than far-away ones). I overcome those two problems with new techniques and am able to create a map with unprecedented sharpness and uniformity, and reveal huge, sharp structures unknown before. We are preparing papers reporting our findings.

Projection vs. Slicing of high dimension space

The figure below illustrates that, compared to the commonly used projection method, slicing the phase space provides much clearer view of the structures in the high dimension phase space. Moreover, the multiple slices also provide brand new information inaccessible with the old projection method, which will finally identify the nature of resonance structures and finish this decades-long debate.

Number Density & Metallicity

Combining the slicing method with metallicity information reveals a few shocking discoveries unknown before. The figure below shows them in another view (horizantal sections of the previous figure), including 1. a tilted under-density; 2. a tilted cliff of metallicity.

Click the plot below for an interactive visualization, again showing the guiding center distribution, sliced with certain epicycle parameters set by the two sliders.

Explanation of coordinates: there are in total 4D for the in-disk motions: (x, y, vx, vy), or equivalently into action-angle variables: (jphi, angle phi) for guiding center motion and (jr, angle r) for the epicycle motion. Large jphi means high angular momentum. Large jr means more eccentric orbit.

Contacts

scheng@ias.edu
+1 443 207 1532
Institute for Advanced Study
Princeton, NJ 08540, USA