Galactoseismology: Discovery of Vertical Waves in the Galactic Disk

TL;DR

This paper provides evidence for vertical wave-like perturbations in the Milky Way's disk, likely caused by interactions with satellite galaxies or dark matter subhalos, revealing new insights into galactic dynamics.

Contribution

It introduces the discovery of vertical waves in the galactic disk and analyzes their potential origins through theoretical modeling and simulations.

Findings

Detected North-South asymmetry in star density and velocity profiles.

Identified wave-like perturbations possibly caused by satellite interactions.

Suggested recent disk-heating event as a cause of the observed waves.

Abstract

We present evidence for a Galactic North-South asymmetry in the number density and bulk velocity of solar neighborhood stars. The number density profile, which is derived from main-sequence stars in the Sloan Digital Sky Survey, shows a (North - South)/(North + South) deficit at |z| ~ 400 pc and an excess at |z| ~ 800 pc. The bulk velocity profile, which is derived from the Sloan Extension for Galactic Understanding and Exploration, shows a gradual trend across the Galactic midplane as well as smaller-scale features. We speculate that the North-South asymmetry, which has the appearance of a wavelike perturbation, is intrinsic to the disk. We explore the physics of this phenomenon through an analysis of the linearized Boltzmann and Poisson equations and through one-dimensional simulations. The perturbation may be excited by the passage of a satellite galaxy or dark matter subhalo through the Galactic disk, in which case we are witnessing a recent disk-heating event.