Abstract
A chemodynamical model of our Galaxy is fitted to data from DR17 of the APOGEE survey supplemented with data from the StarHorse catalogue and Gaia DR3. Dynamically, the model is defined by action-based distribution functions for dark matter and six stellar components plus a gas disc. The gravitational potential jointly generated by the model's components is used to examine the Galaxy's chemical composition within action space. The observational data probably cover all parts of action space that are populated by stars. The overwhelming majority of stars have angular momentum J(phi) > 0 implying that they were born in the Galactic disc. High-alpha stars dominate in a region that is sharply bounded by J(phi) less than or similar to J(phi)(solar). Chemically the model is defined by giving each stellar component a Gaussian distribution in ([Fe/H],[Mg/Fe]) space about a mean that is a linear function of the actions. The model's 47 dynamical parameters are chosen to maximize the likelihood of the data given the model in 72 three-dimensional velocity spaces while its 70 chemical parameters are similarly chosen in five-dimensional chemodynamical space. The circular speed falls steadily from 237 km s(-1) at R = 4 kpc to 218 km s(-1) at R = 20 kpc. Dark matter contributes half the radial force on the Sun and has local density 0.011 M-circle dot pc(-3), there being 24.5 M-circle dot pc(-2) in dark matter and 26.5 M-circle dot pc(-2) in stars within 1.1 kpc of the plane.