Constraining The Milky Way Bar Length using Hercules and Gaia DR3

Author:

Scott Lucchini, Elena D'Onghia, J. Alfonso L. Aguerri

Keyword:

Astrophysics, Astrophysics of Galaxies, Astrophysics of Galaxies (astro-ph.GA)

journal:

date:

2023-05-07 16:00:00

Abstract

The distribution of moving groups in the solar neighborhood has been used to constrain dynamical properties of the Milky Way for decades. Unfortunately, the unique bimodality between the main mode (Hyades, Pleiades, Coma Berenices, and Sirius) and Hercules can be explained by two different bar models -- via the outer Lindblad resonance of a short, fast bar, or via the corotation resonance of a long, slow bar. In this work, we break this degeneracy by using Gaia DR3 to explore the variation of Hercules across Galactic azimuth. We find that Hercules increases in $V_\phi$ and becomes stronger as we move towards the minor axis of the bar, and decreases in $V_\phi$ and becomes weaker as we move towards the major axis of the bar. This is in direct agreement with theoretical predictions of a long, slow bar model in which Hercules is formed by the corotation resonance with stars orbiting the bar's L4/L5 Lagrange points.

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