Yongjun Jiao (L'Observatoire de Paris) - France, November 27, 2023

The rotation curve (RC) is the most accurate tool for estimating the enclosed dynamical mass of the galaxy. In 1925, Lundmark was amongst the first to identify the flat behaviour of disc-galaxy RCs. By the 1970s, several studies confirmed that most spiral galaxies show a flat RC. Extended flat RCs of spiral galaxies can be considered as major evidence of the presence of an extended halo of dark matter (DM) surrounding them. But our position inside the Galactic disc has previously prevented us from establishing an accurate RC of our own Galaxy, the Milky Way (MW).
Thanks to the latest Gaia satellite catalogue from the European Space Agency (ESA), we could establish a new MW RC from its third data release (Gaia DR3) up to 26.5 kpc with a robust analysis of the systematic uncertainties. We find a sharply decreasing RC for the MW, the decrease in velocity between 19.5 and 26.5 kpc is approximately 30 km/s. With this RC, we estimate the MW total mass is 2.06 10^11 Msun. By studying the decrease in RC at large radii, we identify a Keplerian decline in the MW RC between 19 and 26 kpc from the MW centre, while a flat RC is rejected with a significance of 3σ.
In this talk, I will present our analysis of systematic uncertainties based on the previous measurement of MW RC, the estimation of MW total mass and discuss the detection of the Keplerian decline in the MW RC.