A New Method for Determining the Milky Way Bar Pattern Speed

TL;DR

This paper introduces a novel method to estimate the Milky Way's bar pattern speed by analyzing the influence of the bar on local stellar velocity gradients and Oort constants, using numerical simulations and observational data.

Contribution

It presents a new approach combining simulations and observations to accurately determine the Galactic bar's pattern speed and orientation, improving previous models.

Findings

Estimated bar pattern speed: Omega_b/Omega_0=1.87±0.04

Bar angle range: 20° to 45°

Bar's effect on A and B constants is minimal (~2 km/s/kpc) for hot stars

Abstract

Previous work has related the Galactic bar to structure in the local stellar velocity distribution. Here we show that the bar also influences the spatial gradients of the velocity vector via the Oort constants. By numerical integration of test-particles we simulate measurements of the Oort C value in a gravitational potential including the Galactic bar. We account for the observed trend that C is increasingly negative for stars with higher velocity dispersion. By comparing measurements of C with our simulations we improve on previous models of the bar, estimating that the bar pattern speed is Omega_b/Omega_0=1.87\pm0.04, where Omega_0 is the local circular frequency, and the bar angle lies within 20[deg]<phi_0<45[deg]. We find that the Galactic bar affects measurements of the Oort constants A and B less than ~2 km/s/kpc for the hot stars.