Spontaneous generation of bending waves in isolated Milky Way-like discs

Abstract

We study the spontaneous generation and evolution of bending waves in $N$-body simulations of two isolated Milky Way-like galaxy models. The models differ by their disc-to-halo mass ratios, and hence by their susceptibility to the formation of a bar and spiral structure. Seeded from shot noise in the particle distribution, bending waves rapidly form in both models and persist for many billions of years. Waves at intermediate radii manifest as corrugated structures in vertical position and velocity that are tightly wound, morphologically leading, and dominated by the $m=1$ azimuthal Fourier component. A spectral analysis of the waves suggests they are a superposition of modes from two continuous branches in the Galactocentric radius-rotational frequency plane. The lower-frequency branch is dominant and is responsible for the corrugated, leading, and warped structure. Over time, power in this branch migrates outward, lending credence to an inside-out formation scenario for the warp. Our power spectra qualitatively agree with results from linear perturbation theory and a WKB analysis, both of which include self-gravity. Thus, we conclude that the waves in our simulations are self-gravitating and not purely kinematic. These waves are reminiscent of the wave-like pattern recently found in Galactic star counts from the Sloan Digital Sky Survey and smoothly transition to a warp near the disc's edge. Velocity measurements from \textit{Gaia} data will be instrumental in testing the true wave nature of the corrugations. We also compile a list of "minimum requirements" needed to observe bending waves in external galaxies.

Accepted for publication in MNRAS, 15 pages, 10 figures, 1 table

References in corpus (16)

• The Gaia mission
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory
• Outer structure of the Galactic warp and flare: explaining the Canis Major over-density
• Rings and Radial Waves in the Disk of the Milky Way
• The Vertical Structure of the Outer Milky Way HI Disk
• Stellar kinematics across the Hubble sequence in the CALIFA survey: General properties and aperture corrections
• Bending and Breathing Modes of the Galactic Disk
• Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy''
• Galactic Warps Induced By Cosmic Infall
• The Vertical Structure and Kinematics of Grand Design Spirals
• On the Origin of Dynamically Cold Rings Around the Milky Way
• The vertical effects of disc non-axisymmetries from perturbation theory: the case of the Galactic bar
• Galactoseismology and the Local Density of Dark Matter
• Very Thin Disc Galaxies in The SDSS Catalog of Edge-on Galaxies
• Characterizing the Galactic warp with Gaia: I. The tilted ring model with a twist

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• Bending Waves in Velocity Space: a First Look at the THINGS sample