Galactic Bar Resonances Inferred from Kinematically Hot Stars in Gaia EDR3

TL;DR

This study uses Gaia EDR3 data and simulations to identify bar resonance features in the Milky Way, revealing multiple resonance signatures and estimating the bar's pattern speed.

Contribution

It demonstrates that kinematically hot stars reveal prominent resonance features related to the galactic bar, and identifies multiple resonance signatures consistent with two possible pattern speeds.

Findings

Resonance features are more prominent in hot stars' action space.

Two candidate bar pattern speeds are identified: ~34 and 42 km/s/kpc.

Multiple resonance features, including new ones, are observed in Gaia data.

Abstract

Using a numerical simulation of an isolated barred disc galaxy, we first demonstrate that the resonances of the inner bar structure induce more prominent features in the action space distribution for the kinematically hotter stars, which are less sensitive to the local perturbation, such as the transient spiral arms. Then, we analyse the action distribution for the kinematically hotter stars selected from the Gaia EDR3 data as the stars with higher values of radial and vertical actions. We find several resonance features, including two new features, in the angular momentum distribution similar to what are seen in our numerical simulations. We show that the bar pattern speeds of about $\Omega_{\rm bar}\sim34$~km~s$^{-1}$~kpc$^{-1}$ and 42~km~s$^{-1}$~kpc$^{-1}$ explain all these features equally well. The resonance features we find correspond to the inner 4:1, co-rotation, outer 4:1, outer Lindblad and outer 4:3 (co-rotation, outer 4:1, outer Lindblad, outer 4:3 and outer 1:1) resonances, when $\Omega_{\rm bar}\sim34$ (42) km~s$^{-1}$~kpc$^{-1}$ is assumed.