Description
The Gaia spacecraft has brought our Milky Way into focus in an unprecedented way. The synergy with ground-based spectroscopic surveys has provided us with photometry, 6-D phase-space coordinates, and spectra for millions of stars. This rich data has highlighted the presence of departures from dynamical equilibrium, such as the phase-space spiral.
Despite these departures, equilibrium dynamical models can still provide a useful tool for understanding the formation of galaxies. I will show this with two examples using the Milky Way, M31, and Milky Way analogues as case studies. In the first example, I will present how we can use cosmological simulations of galaxies to measure the systematic uncertainties in derived dark matter mass distributions and velocity anisotropies in equilibrium dynamical modelling. In the second example, I will showcase the power of extended distribution functions, or eDFs, in modelling both our Milky Way and Milky Way analogues (MWAs) with integral-field unit data. In the former, eDFs neatly couple the selection function with the age, metallicity, and kinematic distribuions to reveal the intrinsic distributions. In the latter, eDFs offer a natural mechanism for modelling the coupled chemodynamical data encoded in IFU spectra. A final advantage offered by using analytical eDFs is that they can be easily related to aspects of formation history like the star formation history, thus offering a direct way of comparing MWAs.
