Substructure

Engineering

Transient (computer programming)

Galaxy

Astrophysics

Operating system

Computer science

Spiral (railway)

Physics

Mathematics

Astronomy

Mass distribution

Mathematical analysis

Geometry

Logarithmic spiral

Structural engineering

Milky Way

Spiral galaxy

Monthly Notices of the Royal Astronomical Society

The second data release from ESA's Gaia mission has revealed many ridge-like structures in the velocity distribution of the Milky Way. We show that these can arise naturally from winding transient spiral structure that is commonly seen in N-body simulations of disk galaxies. We construct test particle models of the winding spiral structure, and compare the resulting distribution of orbits with the observed two-dimensional velocity distribution in the extended solar neighbourhood and with the distribution of rotational velocities over 8 kpc along the Sun--Galactic-centre--Galactic anti-centre line. We show that the ridges in these observations are well reproduced by the winding spiral model. Additionally, we demonstrate that the transient winding spiral potential can create a Hercules-like feature in the kinematics of the solar neighbourhood, either alone, or in combination with a long-slow bar potential.

Transient spiral structure and the disc velocity substructure in Gaia DR2