The nuclear stellar disc of the Milky Way as a tracer of the Galactic bar

The nuclear stellar disc is a flat dense stellar structure at the heart of the Milky Way. Recent work shows that analogous structures are common in the nuclei of external spiral galaxies, where there is evidence of an age gradient indicating that they form inside-out from gas funnelled to the centre by the galactic bar. Analysing the stellar population of the nuclear disc at different radii, we find an age gradient along the line of sight. We detect the presence of a significant mass (~40% of the total stellar mass) of intermediate-age stars (2-7 Gyr) in the outer regions of the nuclear stellar disc that is not present in its innermost regions, in which ~90% of the stellar mass is older than 7 Gyr. Our results are consistent with an inside-out formation of the nuclear stellar disc, and suggest that the age distribution of the nuclear stellar disc is similar to the one found in external galaxies. This implies that bar-driven processes observed in external galaxies are also at play in the Milky Way. Hence, the nuclear stellar disc is related to the Galactic bar and its properties can give us insight into its age and formation history.