Stellar dynamics around transient co-rotating spiral arms

TL;DR

This study uses N-body/SPH simulations to show that spiral arms in galaxies are transient, co-rotating features that significantly influence stellar migration, challenging the traditional long-lived spiral density wave theory.

Contribution

The paper demonstrates through simulations that spiral arms are transient and co-rotating, providing new insights into stellar migration mechanisms in galaxies.

Findings

Spiral arms are transient, not long-lived structures.

Particles migrate along spiral arms, influenced by their co-rotation.

Strong stellar migration occurs due to sustained acceleration and deceleration by spiral arms.

Abstract

Spiral density wave theory attempts to describe the spiral pattern in spiral galaxies in terms of a long-lived wave structure with a constant pattern speed in order to avoid the winding dilemma. The pattern is consequently a rigidly rotating, long-lived feature. We run an N-body/SPH simulation of a Milky Way-sized barred disk, and find that the spiral arms are transient features whose pattern speeds decrease with radius, in such a way that the pattern speed is almost equal to the rotation curve of the galaxy. We trace particle motion around the spiral arms. We show that particles from behind and in front of the spiral arm are drawn towards and join the arm. Particles move along the arm in the radial direction and we find a clear trend that they migrate toward the outer (inner) radii on the trailing (leading) side of the arm. Our simulations demonstrate that at all radii where there is a co-rotating spiral arm the particles continue to be accelerated (decelerated) by the spiral arm for long periods, which leads to strong migration.