The Milky Way Halo in Action Space

Understand

We analyse the structure of the local stellar halo of the Milky Way using $\sim$ 60000 stars with full phase space coordinates extracted from the SDSS--{\it Gaia} catalogue.

• We display stars in action space as a function of metallicity in a realistic axisymmetric potential for the Milky Way Galaxy.
• The metal-rich population is more distended towards high radial action $J_R$ as compared to azimuthal or vertical action, $J_\phi$ or $J_z$.
• It has a mild prograde rotation $(\langle v_\phi \rangle \approx 25$ km s$^{-1}$), is radially anisotropic and highly flattened with axis ratio $q \approx 0.6 - 0.7$.