Standing on the shoulders of the previous HESTIA project by CLUES collaboration, I lead the new generation of zoom-in simulations for the Local Group - HESTIA-2. We use a broader range of initial conditions constrained by the data from CosmicFlow-2 and -4 catalogues. Here, we also use the state-of-the-art SWIFT code, giving us excellent computational efficiency while dealing with the large 147cMpc box and dense zoom-in region. For the highest resolution runs, we target the mass of star particles to be ~1000 solar masses.
Orbit superposition of Milky Way
Despite the significant advancements in observational data on the Milky Way's stellar populations, which have greatly expanded the volume we can analyze across the Galaxy and beyond, our maps remain heavily obscured by observational strategies and survey selection functions, limiting our ability to fully understand the true structure and distribution of stars within the Galaxy.
​
To finally solve this fundamental problem, I have developed a novel approach aiming to reconstruct the entire Galaxy. This method is built upon the original idea introduced by Schwarzshild in 1979, assuming that a triaxial galaxy can be represented by a superposition of orbits weighted to match the observed light distribution. For the first time, I have extended this approach to the resolved stellar populations of the Milky Way. Using the orbits of real APOGEE stars, together with my colleagues at AIP, Vienna University and Paris Observatory, we have recovered the complete 3D density structure of our Galaxy and obtained the selection-function corrected chemical abundance and age data.
The figure above illustrates how the spatial footprint of APOGEE DR 17 can be extended by using the orbits of real stars integrated within a realistic barred potential of the Milky Way, constrained by other observational data. The significance of weight calculations is emphasized in the left figure below, which compares the density structure derived solely from the orbits with the refined, weighted solution.
The top-right panels highlight the impact of orbit weights on the chemical abundance composition. In these panels, I compare the raw APOGEE star counts in the [Mg/Fe]-[Fe/H] plane with the stellar mass-weighted solution. This approach accounts for the underlying density distribution, enabling a quantitative analysis of the true chemical abundance variations across the Galactic disk and bulge. Notably, the method provides a detailed reconstruction of the bulge stellar populations structure, as illustrated in the bottom-right panel.
To learn more, please take a look at the first three papers describing the approach and the main results concerning the Milky Way disc and the bulge. I am currently working on further extension of the method, aiming to constrain the present-day distribution of dark matter and the assembly history of the Milky Way galaxy.