Vertical density waves in the Milky Way disc induced by the Sagittarius Dwarf Galaxy

TL;DR

This paper investigates how the Sagittarius dwarf galaxy's passage through the Milky Way could have induced vertical density waves in the galactic disk, aligning with recent observations of asymmetries.

Contribution

It demonstrates through simulations that the Sagittarius impact can produce vertical density waves and asymmetries consistent with observations, highlighting the role of satellite mass.

Findings

Vertical waves produce North-South asymmetries.

Vertical oscillations cause radial and azimuthal velocity variations.

Amplitude of velocity variations can reach 8 km/s.

Abstract

Recently, Widrow and collaborators announced the discovery of vertical density waves in the Milky Way disk. Here we investigate a scenario where these waves were induced by the Sagittarius dwarf galaxy as it plunged through the Galaxy. Using numerical simulations, we find that the Sagittarius impact produces North-South asymmetries and vertical wave-like behavior that qualitatively agrees with what is observed. The extent to which vertical modes can radially penetrate into the disc, as well as their amplitudes, depend on the mass of the perturbing satellite. We show that the mean height of the disc is expected to vary more rapidly in the radial than in the azimuthal direction. If the observed vertical density asymmetry is indeed caused by vertical oscillations, we predict radial and azimuthal variations of the mean vertical velocity, correlating with the spatial structure. These variations can have amplitudes as large as 8 km/s.