Galactoseismology in cosmological simulations: Vertical perturbations by dark matter, satellite galaxies and gas

TL;DR

This study uses a high-resolution cosmological simulation to analyze how dark matter, satellite galaxies, and gas infall induce vertical perturbations and bending modes in a Milky Way-like galaxy's disk over 6 billion years.

Contribution

It identifies multiple agents, including satellites, dark matter, and gas, that collectively cause complex vertical disturbances in galactic disks within a cosmological context.

Findings

Complex bending patterns vary with radius and time.

Satellite infall causes disk tilt and anisotropic gas accretion.

Multiple agents, including dark matter and gas, influence disk bending and phase spirals.

Abstract

Only recently, complex models that include the global dynamics from dwarf satellite galaxies, dark matter halo structure, gas infalls, and stellar disk in a cosmological context became available to study the dynamics of disk galaxies such as the Milky Way (MW). We use a MW model from a high-resolution hydrodynamical cosmological simulation named GARROTXA to establish the relationship between the vertical disturbances seen in its galactic disk and multiple perturbations, from the dark matter halo, satellites and gas. We calculate the bending modes in the galactic disk in the last 6 Gyr of evolution. To quantify the impact of dark matter and gas we compute the vertical acceleration exerted by these components onto the disk and compare them with the bending behavior with Fourier analysis. We find complex bending patterns at different radii and times, such as an inner retrograde mode with high frequency, as well as an outer slower retrograde mode excited at different times. The amplitudes of these bending modes are highest during the early stages of the thin disk formation and reach up to 8.5 km s-1 in the late disk evolution. We find that the infall of satellite galaxies leads to a tilt of the disk, and produces anisotropic gas accretion with subsequent star formation events, and supernovae, creating significant vertical accelerations onto the disk plane. The misalignment between the disk and the inner stellar/dark matter triaxial structure, formed during the ancient assembly of the galaxy, creates a strong vertical acceleration on the stars. We conclude that several agents trigger the bending of the stellar disk and its phase spirals in this simulation, including satellite galaxies, dark sub-halos, misaligned gaseous structures, and the inner dark matter profile, which coexist and influence each other, making it challenging to establish direct causality.