Kinematic structure of the Milky Way galaxy, near the spiral arm tangents

TL;DR

This paper examines the kinematic structure of the Milky Way near spiral arm tangents, comparing observed velocities with density wave theory predictions, and confirms some theoretical expectations about velocity offsets.

Contribution

It provides observational evidence supporting density wave theory predictions of velocity offsets near spiral arm tangents in the Milky Way.

Findings

Observed velocity offsets of about 20 km/s support density wave theory.

Velocity offsets are consistent with theoretical predictions when larger than error margins.

The study estimates the time for the Sun to reach the next spiral arm.

Abstract

We compare the observed radial velocity of different arm tracers, taken near the tangent to a spiral arm. A slight difference is predicted by the density wave theory, given the shock predicted at the entrance to the inner spiral arm. In many of these spiral arms, the observed velocity offset confirms the prediction of the density wave theory (with a separation between the maser velocity and the CO gas peak velocity, of about 20 km/s) - when the observed offset is bigger than the error estimates. The time to reach the next spiral arm is given.