A Kiloparsec-Scale Nuclear Stellar Disk in the Milky Way as a Possible Explanation of the High Velocity Peaks in the Galactic Bulge

TL;DR

This study combines observational data and simulations to suggest that a kiloparsec-scale nuclear stellar disk in the Milky Way explains the high velocity peaks observed in the galactic bulge.

Contribution

It provides the first evidence linking a nuclear stellar disk to high velocity peaks in the Milky Way's bulge using combined observational and simulation data.

Findings

Detection of a second high-velocity peak in the LOSVDs at the galactic center.

Simulation results support the existence of a thin, rapidly rotating nuclear disk.

The nuclear disk is oriented perpendicular to the galactic bar and formed from gas on x2 orbits.

Abstract

The Apache Point Observatory Galactic Evolution Experiment has measured the stellar velocities of red giant stars in the inner Milky Way. We confirm that the line of sight velocity distributions (LOSVDs) in the mid-plane exhibit a second peak at high velocities, whereas those at |b| = 2degrees do not. We use a high resolution simulation of a barred galaxy, which crucially includes gas and star formation, to guide our interpretation of the LOSVDs. We show that the data are fully consistent with the presence of a thin, rapidly rotating, nuclear disk extending to ~1 kpc. This nuclear disk is orientated perpendicular to the bar and is likely to be composed of stars on x2 orbits. The gas in the simulation is able to fall onto such orbits, leading to stars populating an orthogonal disk.