Kinematics of the Galaxy from Young Open Star Clusters with Data from the Gaia EDR3 Catalogue

TL;DR

This study analyzes the kinematics of young open star clusters using Gaia EDR3 data to determine Galactic rotation parameters and spiral density wave characteristics, providing precise measurements of the Galaxy's rotation and spiral structure.

Contribution

It presents new measurements of Galactic rotation and spiral wave parameters based on a large sample of young open star clusters from Gaia EDR3, focusing on the youngest clusters for improved accuracy.

Findings

Galactic rotation parameters are consistent across different cluster ages.

The circular velocity at the solar neighborhood is approximately 227 km/s.

Spiral density wave amplitudes and wavelengths are quantified for a four-armed pattern.

Abstract

We have analyzed the kinematics of open star clusters (OSCs) with the proper motions and distances calculated by Hao et al. based on Gaia EDR3 data. The mean line-of-sight velocities are known for a number of clusters from this list. We show that the Galactic rotation parameters determined from samples of OSCs with various ages are in good agreement between themselves. The most interesting results have been obtained from a sample of 967 youngest OSCs with a mean age of 18 Myr. In particular, we have found the following parameters of the angular velocity of Galactic rotation using only their proper motions and distances: $\Omega_0 =28.01\pm0.15$ km s$^{-1}$ kpc$^{-1},$ $\Omega^{'}_0=-3.674\pm0.040$ km s$^{-1}$ kpc$^{-2},$ and $\Omega^{''}_0=0.565\pm0.023$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center here is $V_0=226.9\pm3.1$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.1\pm0.1$ kpc. The parameters of the spiral density wave have been determined from the space velocities of 233 young clusters. The amplitudes of the radial and tangential velocity perturbations produced by the spiral density wave are $f_R=9.1\pm0.8$ km s$^{-1}$ and $f_\theta=4.6\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $\lambda_R=3.3\pm0.5$ kpc and $\lambda_\theta=2.6\pm0.6$ kpc for the the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave has been found to be $(\chi_\odot)_R\approx-180^\circ$.