Rotation curve of the Milky Way from Classical Cepheids

TL;DR

This study constructs the most accurate rotation curve of the Milky Way beyond 12 kpc using a large sample of Classical Cepheids with precise distances, Gaia data, and a simple Galactic rotation model.

Contribution

It provides the first detailed, accurate rotation curve of the Milky Way up to 20 kpc using Classical Cepheids and Gaia data, improving understanding of Galactic dynamics.

Findings

Rotation speed of the Sun is 233.6 km/s.

The rotation curve is nearly flat between 4 and 20 kpc.

This is the most accurate rotation curve beyond 12 kpc to date.

Abstract

Flat rotation curves of spiral galaxies are considered as an evidence for dark matter, but the rotation curve of the Milky Way is difficult to measure. Various objects were used to track the rotation curve in the outer parts of the Galaxy, but most studies rely on incomplete kinematical information and inaccurate distances. Here, we use a sample of 773 Classical Cepheids with precise distances based on mid-infrared period-luminosity relations coupled with proper motions and radial velocities from Gaia to construct the accurate rotation curve of the Milky Way up to the distance of ~20 kpc from the Galactic center. We use a simple model of Galactic rotation to measure the rotation speed of the Sun Theta_0 = 233.6 +/- 2.8 km/s, assuming a prior on the distance to the Galactic center R_0 = 8.122 +/- 0.031 kpc from the Gravity Collaboration. The rotation curve at Galactocentric distances 4 < R < 20 kpc is nearly flat with a small gradient of -1.34 +/- 0.21 km/s/kpc. This is the most accurate Galactic rotation curve at distances R > 12 kpc constructed so far.