Spiral-induced velocity and metallicity patterns in a cosmological zoom simulation of a Milky Way-sized galaxy

TL;DR

This study uses a high-resolution cosmological simulation to demonstrate that spiral arms induce large-scale streaming motions and metallicity variations in a Milky Way-sized galaxy, which are observable with current instruments.

Contribution

It is the first to show that spiral arms in a cosmological environment cause systematic velocity and metallicity patterns, linking galaxy dynamics to observable signatures.

Findings

Spiral arms drive large-scale streaming motions in the galaxy.

Systematic azimuthal metallicity variations are associated with spiral arms.

These signatures are detectable with current integral field spectroscopy instruments.

Abstract

We use a high resolution cosmological zoom simulation of a Milky Way-sized halo to study the observable features in velocity and metallicity space associated with the dynamical influence of spiral arms. For the first time, we demonstrate that spiral arms, that form in a disc in a fully cosmological environment with realistic galaxy formation physics, drive large-scale systematic streaming motions. In particular, on the trailing edge of the spiral arms the peculiar galacto-centric radial and azimuthal velocity field is directed radially outward and azimuthally backward, whereas it is radially inward and azimuthally forward on the leading edge. Owing to the negative radial metallicity gradient, this systematic motion drives, at a given radius, an azimuthal variation in the residual metallicity that is characterised by a metal rich trailing edge and a metal poor leading edge. We show that these signatures are theoretically observable in external galaxies with Integral Field Unit instruments such as VLT/MUSE, and if detected, would provide evidence for large-scale systematic radial migration driven by spiral arms.