Resonant Orbits and the High Velocity Peaks Towards the Bulge

Abstract

We extract the resonant orbits from an N-body bar that is a good representation of the Milky Way, using the method recently introduced by Molloy et al. (2015). By decomposing the bar into its constituent orbit families, we show that they are intimately connected to the boxy-peanut shape of the density. We highlight the imprint due solely to resonant orbits on the kinematic landscape towards the Galactic centre. The resonant orbits are shown to have distinct kinematic features and may be used to explain the cold velocity peak seen in the APOGEE commissioning data (Nidever at al., 2012). We show that high velocity peaks are a natural consequence of the motions of stars in the 2:1 orbit family and that stars on other higher order resonances can contribute to the peaks. The locations of the peaks vary with bar angle and, with the tacit assumption that the observed peaks are due to the 2:1 family, we find that the locations of the high velocity peaks correspond to bar angles in the range 10 < theta_bar < 25 (deg). However, some important questions about the nature of the peaks remain, such as their apparent absence in other surveys of the Bulge and the deviations from symmetry between equivalent fields in the north and south. We show that the absence of a peak in surveys at higher latitudes is likely due to the combination of a less prominent peak and a lower number density of bar supporting orbits at these latitudes.

7 Figures, 1 Table, Now includes figures & discussion of higher order resonances, Minor revisions to text throughout, Conclusions unchanged

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• Modelling the Galactic bar using OGLE-II Red Clump Giant Stars
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Cited by in corpus (20)

• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
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• The stellar mass distribution of the Milky Way's bar: an analytic model
• The Milky Way's nuclear stellar disc: A dynamically cool and metal-rich component formed from the Central Molecular Zone?
• Jeans modelling of the Milky Way's nuclear stellar disc
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics
• The Gaia-ESO survey: Metal-rich bananas in the bulge
• The orbital structure of a tidally induced bar
• Mapping the Three-Dimensional "X-Shaped Structure" in Models of the Galactic Bulge
• Predicted Stellar Kinematics of a Kiloparsec-Scale Nuclear Disc (or Ring) in the Milky Way
• Mapping the tilt of the Milky Way bulge velocity ellipsoids with ARGOS and $Gaia$ DR2
• Signatures of the Galactic bar on stellar kinematics unveiled by APOGEE
• Understanding the velocity distribution of the Galactic Bulge with APOGEE and Gaia
• Chemical abundances and ages of the bulge stars in APOGEE high-velocity peaks
• A new look at the kinematics of the bulge from an N-body model
• Spectroscopic Observations of Obscured Populations in the Inner Galaxy: 2MASS-GC02, Terzan 4, and the 200 km/s stellar peak
• Models of Bars with Exponential Density Profiles
• Signatures of the Galactic bar in high-order moments of proper motions measured by Gaia
• Self-consistent modelling of the Milky Way's Nuclear Stellar Disc