Did Sgr cause the vertical waves in the solar neighbourhood?

Abstract

The vertical distribution of stars in the solar neighbourhood is not in equilibrium but contains a wave signature in both density and velocity space originating from a perturbation. With the discovery of the phase-space spiral in Gaia data release 2, determining the origin of this perturbation has become even more urgent. We develop and test a fast method for calculating the perturbation from a passing satellite on the vertical component of a part of a disc galaxy. This fast method allows us to test a large variety of possible perturbations to the vertical disc very quickly. We apply our method to the range of possible perturbations to the solar neighbourhood stemming from the recent passage of the Sagittarius dwarf galaxy (Sgr), varying its mass, mass profile, and present-day position within their observational uncertainties, and its orbit within different realistic models for the Milky Way's gravitational potential. We find that we are unable to reproduce the observed asymmetry in the vertical number counts and its concomitant breathing mode in velocity space for any plausible combination of Sgr and Milky-Way properties. In all cases, either the amplitude or the perturbation wavelength of the number-count asymmetry and of the oscillations in the mean vertical velocity produced by the passage of Sgr is in large disagreement with the observations from Gaia DR2. We conclude that Sgr cannot have caused the observed oscillations in the vertical disc or the Gaia phase-space spiral.

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• Swing Amplification and the Gaia Phase Spirals
• Which Milky Way masses are consistent with the slightly declining 5-25 kpc rotation curve?
• The AMBRE Project: Solar neighbourhood chemodynamical constraints on Galactic disc evolution
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• The Milky Way, Coming into Focus: Precision Astrometry Probes its Evolution, and its Dark Matter
• Ripples spreading across the Galactic disc. Interplay of direct and indirect effects of the Sagittarius dwarf impact
• Radial Wave in the Galactic Disk: New Clues to Discriminate Different Perturbations
• The pattern speeds of vertical breathing waves
• Characterizing the 3D Kinematics of Young Stars in the Radcliffe Wave
• Arm Tangents and the spiral structure of the Milky Way ; the Age Gradient
• Two-point correlation function studies for the Milky Way: discovery of spatial clustering from disk excitations and substructure
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• Inferring Time-Dependent Distribution Functions from Kinematic Snapshots
• Resolving local and global kinematic signatures of satellite mergers with billion particle simulations