Detection of the Keplerian decline in the Milky Way rotation curve

TL;DR

Using Gaia DR3 data, the study precisely maps the Milky Way's rotation curve, revealing a Keplerian decline between 19 and 26.5 kpc, and revising the galaxy's total mass downward, challenging previous flat rotation assumptions.

Contribution

This work provides the first clear evidence of a Keplerian decline in the Milky Way's rotation curve using Gaia DR3 data, refining mass estimates and reducing uncertainties.

Findings

Detected a Keplerian decline in the rotation curve between 19 and 26.5 kpc.

Revised the total mass of the Milky Way to approximately 2.06 x 10^{11} solar masses.

Rejected a flat rotation curve with 3σ significance.

Abstract

Our position inside the Galactic disc had prevented us from establishing an accurate rotation curve, until the advent of Gaia, whose third data release (Gaia DR3) made it possible to specify it up to twice the optical radius. We aim to establish a new rotation curve of the Galaxy from the Gaia DR3, by drastically reducing uncertainties and systematics, and with the goal to provide a new estimate of the mass of the Galaxy. We have compared different estimates, established a robust assessment of the systematic uncertainties, and addressed differences in methodologies, particularly regarding distance estimates. This results in a sharply decreasing rotation curve for the Milky Way, the decrease in velocity between 19.5 and 26.5 kpc is approximately 30 km s$^{-1}$. We have identified, for the first time, a Keplerian decline of the rotation curve, starting at $\sim$ 19 kpc and up to $\sim$ 26.5 kpc from the Galaxy center, while a flat rotation curve is rejected with a significance of 3$\sigma$. The total mass is revised downwards to $2.06^{+0.24}_{-0.13}\times 10^{11}\ M_{\odot}$, in agreement with an absence of significant mass increase at radii larger than 19 kpc. The upper limit of the total mass was evaluated by considering the upper values of velocity measurements, which leads to a strict, unsurpassable, limit of $5.4\times 10^{11}\ M_{\odot}$.