Analysis of Galactic Rotation from Masers based on a Nonlinear Oort Model

TL;DR

This study uses a nonlinear Oort model to analyze Galactic masers, estimating the solar distance to the Galactic center and revealing nonlinearities and wave patterns in the Galaxy's three-dimensional kinematics.

Contribution

It introduces a nonlinear model for Galactic rotation analysis that accurately estimates the solar Galactocentric distance and identifies velocity waves in the Galaxy's structure.

Findings

Estimated solar Galactocentric distance Ro=8.3+/-0.4 kpc.

Detected a 3 kpc wavelength velocity wave with 10 km/s amplitude.

Found significant nonlinearities only in the xy plane due to Galactic rotation.

Abstract

Based on data on Galactic masers with measured trigonometric parallaxes, we have tested a nonlinear model of Galactic rotation using generalized Oort formulas. This model is shown to yield pretty good results up to heliocentric distances of 3--4 kpc. The main feature of the method is the possibility of estimating the solar Galactocentric distance Ro. This distance has been found by analyzing approximately 60 masers to be Ro=8.3+/-0.4 kpc. Our study of the three-dimensional kinematics of more than 100 masers based on the Ogorodnikov--Milne model has shown that significant nonlinearities are present only in the xy plane (rotation around the Galactic z axis) due to the peculiarities of the Galactic rotation curve. No significant linear dependences have been found in the xz and yz planes. We show the presence of a wave in the velocities w as a function of coordinate x or distance R with a wavelength of 3 kpc and an amplitude of 10 km/s. The wave is particularly prominent in the Local and Perseus arms.