Is the Milky Way ringing? The hunt for high velocity streams

TL;DR

This study uses simulations and semi-analytical models to explain high velocity streams in the Milky Way's Solar neighborhood, suggesting a past galactic perturbation around 1.9 billion years ago, possibly linked to bar formation.

Contribution

It introduces a semi-analytical approach to model velocity streams and links observed features to a historical galactic perturbation event.

Findings

Identifies multiple high velocity streams matching observations.

Predicts four new velocity features not previously observed.

Estimates a significant galactic perturbation occurred ~1.9 Gyr ago.

Abstract

We perform numerical simulations of a stellar galactic disk with initial conditions chosen to represent an unrelaxed population which might have been left following a merger. Stars are unevenly distributed in radial action angle, though the disk is axisymmetric. The velocity distribution in the simulated Solar neighborhood exhibits waves traveling in the direction of positive v, where u,v are the radial and tangential velocity components. As the system relaxes and structure wraps in phase space, the features seen in the uv-plane move closer together. We show that these results can be obtained also by a semi-analytical method. We propose that this model could provide an explanation for the high velocity streams seen in the Solar neighborhood at approximate v in km/s, of -60 (HR 1614), -80 (Arifyanto and Fuchs 2006), -100 (Arcturus), and -160 (Klement et al. 2008). In addition, we predict four new features at v ~ -140, -120, 40 and 60 km/s. By matching the number and positions of the observed streams, we estimate that the Milky Way disk was strongly perturbed ~1.9 Gyr ago. This event could have been associated with Galactic bar formation.