Distribution functions for the Milky Way

Understand

Analytic distribution functions (DFs) for the Galactic disc are discussed.

• The DFs depend on action variables and their predictions for observable quantities are explored under the assumption that the motion perpendicular to the Galactic plane is adiabatically invariant during motion within the plane.
• A promising family of DFs is defined that has several adjustable parameters.
• A standard DF is identified by adjusting these parameters to optimise fits to the stellar density in the column above the Sun, and to the velocity distribution of nearby stars and stars ~1 kpc above the Sun.