Detection of the Keplerian decline in the Milky Way rotation curve

Abstract

Our position inside the Galactic disc has previously prevented us from establishing an accurate rotation curve (RC). The advent of Gaia and its third data release (Gaia DR3) made it possible to specify the RC up to twice the optical radius. We aim to establish a new RC of the Galaxy from the Gaia DR3 by drastically reducing systematic uncertainties. Our goal is to provide a new estimate of the mass of the Galaxy. We compared different estimates, established a robust assessment of the systematic uncertainties, and addressed differences in methodologies, particularly regarding distance estimates. We find a sharply decreasing RC for the Milky Way; the decrease in velocity between 19.5 and 26.5 kpc is approximately 30 km s−1. We identify, for the first time, a Keplerian decline of the RC, starting at ∼19 kpc and ending at ∼26.5 kpc from the Galaxy centre, while a flat RC is rejected with a significance of 3σ. The total mass is revised downwards to 2.06−0.13+0.24 × 1011 M⊙, which is in agreement with the absence of a significant mass increase at radii larger than 19 kpc. We evaluated the upper limit on the total mass by considering the upper values of velocity measurements, which leads to a strict, unsurpassable limit of 5.4 × 1011 M⊙.